Answer: The answer is indded A. Before the family left for the summer, Susan made sure her kids watered their plants, packed their bags, and cleaned their rooms.
Step-by-step explanation:
Parallelism or parallel structure consists of the repetition of a certain grammatical structure inside a sentence. The purpose of such repetition is to avoid confusion, making the speech clear, interesting, and easy to be understood.
The mistake we can find in the sentence is the fact that the last action listed uses a different subject (their rooms) than the two actions before it (her kids). In order to correct it, we must change the last clause so that it uses the same subject as the others:
Before the family left for the summer, Susan made sure her kids watered their plants, packed their bags, and their rooms were clean.
Before the family left for the summer, Susan made sure her kids watered their plants, packed their bags, and cleaned their rooms.