3. With its plan to develop seven and a half acres of shore land, Cleveland is but one of a large number of communities on the Great Lakes that is looking to its waterfront as a way to improve the quality of urban life and attract new businesses.

(A) is looking to its waterfront as a way to improve the quality of urban life and attract

(B) is looking at its waterfront to improve the quality of urban life and attract

(C) are looking to their waterfronts to improve the quality of urban life and attract

(D) are looking to its waterfront as a way of improving the quality of urban life and attracting

(E) are looking at their waterfronts as a way they can improve the quality of urban life and attract

Key thing to notice here: "Cleveland" is the subject of the first "is" in the sentence, but "communities on the Great Lakes" is the subject of the second "is/are". The entire phrase "that is/are looking ... businesses" describes these communities. So there are a bunch of communities on the Great Lakes that ARE interested in improving THEIR waterfronts, and Cleveland is one of them.

So we can eliminate any answer choices with "is" and "its". This leaves C and E. Of these two, C uses less words and the preferable "looking to". So the correct answer is C.

4. Young female ballet dancers and gymnasts sometimes fail to maintain good eating habits caused by the desire to be as thin as possible.

(A) Young female ballet dancers and gymnasts sometimes fail to maintain good eating habits caused by the desire to be as thin as possible.

(B) Good eating habits sometimes fail to be maintained by young female ballet dancers and gymnasts caused by desiring to be as thin as possible.

(C) Because they desire to be as thin as possible, good eating habits are sometimes not maintained by young female ballet dancers and gymnasts.

(D) Because they desire to be as thin as possible, young female ballet dancers and gymnasts sometimes fail to maintain good eating habits.

(E) Young female ballet dancers and gymnasts sometimes fail to maintain good eating habits because they desire to be as thin as possible

We need to avoid modifier errors here - remember: modifiers describe the noun closest to them. The meaning we want to create is that the desire to be as thin as possible causes a failure to maintain good eating habits.

A. "caused by the desire to be as thin as possible" describes "good eating habits". Are good eating habits caused by the desire to be super thin? No. Eliminate.
B. "caused by desiring to be as thin as possible" describes "you female ballet dancers and gymnasts". People aren't caused by a desire to be thin. Eliminate.
C. "Because they desire to be as thin as possible" describes "good eating habits". Do habits want to be thin? No. Eliminate.
D. "Because they desire to be as thin as possible" describes "young female ballet dancers and gymnasts". This makes sense - these people want to be super thin, and this causes them to eat poorly. Keep.
E. "they" in "because they desire to be as thing as possible" is somewhat ambiguous - is it the "young female ballet dancers and gymnasts" who want to be super thin, or is it the "good eating habits" that want to be super thin? Ambiguous pronouns aren't always a good enough reason to eliminate an answer choice on their own - sometimes correct answers on GMAT problems will have ambiguous pronouns, but all of the wrong answer choices will have something major wrong with them. However, if we have two answer choices with nothing major wrong with them, the answer choice without an ambiguous pronoun is the better option. Eliminate.

This leaves D as the correct answer.