The correct pronoun will be a) it
It corresponds to the subject (a convoy) in third person, singular. In this case, it refers to the convoy which successfully arrived to its destination.
Answer:
The correct answer is IT. A convoy of trucks carried supplies to the area devastated by a natural disaster; despite treacherous conditions, it successfully arrived.
Explanation:
The correct pronoun to complete the sentence is IT, it replaces the noun "a convoy of trucks" singular pronoun in third person.
