Following are the explanations and answers for sentence examples:
1--The correct answer is c because the subject of the sentence--both luck and hard work--is clearly plural in structure and idea and therefore requires the plural verb lead.
2--The correct answer is c. A is incorrect because it contains a plural subject--dogs, monkeys and rabbits--but is followed by the singular verb is. B is incorrect because the verb following the relative pronoun which is singular and should be plural.
3--In sentences using correlative conjunctions like neither . . . nor or either . . . or, the noun closest to the verb governs whether the verb is singular or plural. In this case, because the noun is senator (singular), the verb form must also be singular--wants. If representatives and senator were reversed, the verb form would be plural--want.
4--All of the choices are incorrect: a is incorrect because the relative pronoun which is used to refer to inanimate things or to collective nouns referring to people (like family, class, audience); b is incorrect because the prepositional phrase of whom should be replaced by the nominative case pronoun who; c is incorrect because the pronoun whom is in the objective case and, as in b, should be the nominative case who.
5--All of the choices are incorrect: in a., the pronoun his can logically refer to either coach or quarterback; b is also incorrect because the writer clearly means to say that the interception is the quarterback's fault, not the coach's fault, but, because the quotation represents the coach's speech, it states that the coach is taking the blame for the interception; c, like a, has what is called an ambiguous referent--in other words, we can't tell if the coach takes responsibility for the interception or if he blames the quarterback.
6--The correct answer is b. Choice a is incorrect because the writer has used a pronoun--they--but there is no noun in the sentence to which they logically refers. Likewise, c is incorrect because the writer has again used they (twice), but there is no way to know who they are--they could be French, German, Americans, anyone, including Canadians.
7--This question is similar to 6 in that the writer's use of they in a and b creates an ambiguity because there is no noun in the sentence to which they refers. The correct choice is c because it states without ambiguity that the multimedia room is in the library.
8--All are incorrect because a and c do not make clear whether it's the doctor or Jim who has six months to live, and b is clearly illogical because it is unlikely that the doctor has six months to live.
9--All are incorrect: a is worded as a question but is not punctuated with a question mark, and there are missing words between papers and accurate; b is incorrect because the title of the journal Nature is not in italics, and Wikipedia, the title of an online encyclopedia, should also be in italics, and the trailing verb is is unnecessary, as is the exclamation point, which should be used in very rare cases (like a shout or an exclamation); c, like b, fails to italicize Nature and Wikepedia, ends improperly with a question mark (the sentence is a statement), and the prepositional phrase in relation to should be changed to as the.