It's either C or D. hope this helps!
The answer is D. For A to work it would have to be "Am I going with you to the grocery store? For B to work it would have to be "You children have to wash your hands after playing outside." For C to work it would have to be "Don't you want to know whats inside the box?" Generally the best way to solve these problems is through process of elimination, just so that you're sure that your answer is correct.
D, a prepositional phrase will usually have indicators such as “at” and then followed by verbs or nouns, like “our first social even”
I believe that Mollie is never again mentioned in <em>Animal Farm </em>because the other animals do not want to remember that not everyone agrees with their new way of life.
Hope it helps!