阅读下面短文，掌握其大意，然后从各题所给的四个选项中选出可以填入空白处的最佳选项。

Last Sunday our class went on a trip to the zoo. We ___ at the school gate at seven and took a bus there. There were many kinds of animals in the zoo. The monkeys were the most ___ of all; they jumped up and down all the time. The guide told us that some wild animals were in great ___ and we should protect them. We took a lot of photos and ___(4) home at about five in the afternoon. Everyone said it was a really ___ trip.

【第4空】