Which of these is a compound sentence?
A. Officer Juarez had a kind, friendly smile.
B. In October, the leaves begin to change colors.
C. Ami went to the store, but she forgot to buy milk.
D. Before the train departed, the passengers boarded.
It's a compound sentence, because it features 2 different subjects. The first subject was her going to the store the second subject was of her forgetting milk.
