I've written before about how preparation material for the SAT writing section sometimes presents an over-simplified view of grammar that can get you into linguistic trouble. Here's another case in point: The following question appears in a Kaplan practice SAT (12 Practice Tests for the SAT 2009 Edition, p. 589):

Although talent may be a crucial element on the road to fame, it is difficult to succeed without a highly developed work ethic. (A) it is difficult to succeed without a highly developed work ethic (B) being difficult to succeed without a highly developed work ethic (C) the difficulty in succeeding is when you don't have highly developed work ethic (D) without a highly developed work ethic, succeeding is difficult (E) it will be difficult to succeed without a highly developed work ethic

According to the answer key, D is the right answer, a choice that, although I can accept as grammatical, I find frankly bizarre, as placing the prepositional phrase "without...ethic" before the matrix clause is awkward. Here's the explanation given (p. 620):

Pronouns are frequently used without antecedents in everyday speech, but such usage will be incorrect on the SAT. In this sentence, the pronoun it has no antecedent. Choice (D) eliminates the ambiguous pronoun without introducing any additional errors.

This statement makes an explicit claim about a grammatical rule followed on the SAT. Implicitly, it contrasts casual spoken usage with standard written English. The message is, "hey, I know the original sounds right, but this is really the way you have to do it for the test." Unfortunately for the writer of this question (but fortunately for common sense) the claim is mistaken both as a general principle of Standard English and as a specific rule followed by the SAT. If we take the claim here literally, it is clearly untrue. The explanation seems to assert that all pronouns must have antecedents. If not, they are ambiguous. But some pronouns, for example I and you, are understood not by reference to a noun phrase (the antecedent) but relative to the context of the utterance. Linguists call this kind of reference deixis. It is distinct from the pronoun-antecedent relationship, which is technically known as anaphora. A pronoun that has an antecedent is called an anaphor, but pronouns need not be anaphors. (And although it's not directly relevant to my current point, there are things other than pronouns that can be anaphors too.) Even if we interpret the Kaplan question writer charitably, and interpret the assertion to be narrowly focused on the pronoun used in this particular sentence, it, the claim is still false. While it frequently does function as an anaphor, there are a number of extremely common, and unquestionably standard, constructions in which it serves as a dummy subject, one that has no particular reference. The following examples represent some of the most common constructions: (1) It is cloudy. (2) It was my brother who wrecked the car. (3) It is scandalous that many English teachers cannot identify the passive voice. All of these are standard English. In none of them does it refer to anything in particular. Sentence (3) is an instance of extraposition, in which an item that can be identified as the semantic subject of the sentence is pushed to the end of the clause and the grammatical subject is filled by it. You can identify extraposed sentences because they can be rearranged into a version where the extraposed subject becomes the actual grammatical subject: (3a) That many English teachers cannot identify the passive voice is scandalous. The underlined clause in the Kaplan question is also an extraposed construction. Notice that we can easily rewrite it in a non-extraposed form: "to succeed without a highly developed work ethic is difficult." Because the it in an extraposed clause isn't supposed to refer to anything, it hardly makes sense to call it ambiguous, which would imply that there's some confusion over the intended referent. It's also ridiculous to assert that this is non-standard English. If it is, than so is one of the most famous sentences in English literature: the opening of Jane Austin's Pride and Prejudice:

It is a truth universally acknowledged that a single man in possession of a good fortune must be in want of a wife.

OK, you may be saying to yourself, I'll accept that extraposed clauses are Standard English, but maybe this is still a rule you need to follow for the SAT, even if it's silly. That too is utter nonsense. It took me only five minutes to find counter-examples in official College Board material. In The Official SAT Study Guide, practice test 8, there are no less than three questions within the span of two pages that contain dummy it. For example

16. Although the details of the contract has not yet been announced, it is likely that union negotiators accepted the proposed training program for newly hired workers. No error (p. 846)

See questions 15 and 29 in the same section for the other two instances. The presence of a clear subject-verb agreement error elsewhere in the sentence demonstrates beyond question that the College Board doesn't think it here is in any way problematic. Moreover, the structure in this sentence is quite similar to the one in the Kaplan sentence: a subordinate clause with although followed by an extraposed clause. Although you could probably rewrite this sentence to be acceptable without extraposition, (A) is definitely grammatical and is the best among the alternatives given. In short, the Kaplan question is another example of someone misunderstanding a grammatical principle, making unsupported assertions about the way you must write, and producing awkward, unidiomatic prose in an attempt to avoid a non-existent problem.