Answer:
OD. When the family saw the storm coming, they decided to take their picnic inside.
Explanation:
Pronoun agreement refers to the rule of having or applying the same number for a pronoun and its antecedents. In other words, a singular antecedent will have a singular pronoun and a plural antecedent will have a plural pronoun.
In the given sentences, sentence D has the correct pronoun agreement. The subject "family" is a plural number, therefore the use of the pronoun "they" and "their" for the family is correct.
Thus, the correct answer is option D.