Answer:
B). Their.
Explanation:
As per the question, the word 'their' completes the given sentence correctly as it is syntactically and semantically the correct pronoun to denote the plural antecedent 'Jon and Tucker' and accomplish the meaning and grammar of the sentence appropriately. The final sentence reads as:
'Jon and Tucker walked for miles in the hot sun, carrying their heavy backpacks with them.'
The other options are incorrect as they fail to accomplish the meaning of the sentence appropriately. Option A('theirs) exemplifies the inappropriate pronoun to replace the antecedent while option C i.e. 'they'are' signifies contraction merely. Thus, option B is the correct answer.
