1. Due to his high metabolism rate, Jeff can eat anything he wants and barely gain any weight at all.
The sentence is a compound sentence connecting two independent clauses by a conjunction ‘and’. The two clauses each must have there own working verbs. Read with the subject, Jeff, a third person singular noun, the verb should be ‘barely gains’ as in B rather than ‘barely gain’ as in A.
2. Brad wanted to go to fish with his dad, but they had to wait
because it was a dreary and rainy day.
a) wanted to go to fish with his dad, but they had to wait – but they is wrong pronoun for the singular subject Brad
b) and his dad were wanting to go to fish, but they were waiting – grammatically correct, and the best of the lot
c) were wanting to go fishing, but they had to wait: –Brad were wanting? Problem in S –V number agreement; again, they can not refer to Brad
d) wanted going to fish with his dad, but they were waiting - they can not refer to Brad
e) planned on going fishing with his dad, but it needed waiting; no antecedent for ‘it’
3. Just before the test began, Alexander asked his classmate if he might be borrowing an extra sheet of paper.
The pronoun ambiguity of ‘he’ is a problem in every choice other than D. But D in addition to being in passive voice does not clarify from whom or by whom a sheet of paper might be borrowed. So C is the best as such
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