这几道题都是选择题我有一些疑问用红笔打出的都是正确答案

这几道题都是选择题我有一些疑问用红笔打出的都是正确答案
There is a bag of apples on the ground.为什么不是苹果在书包里
Three years has passed since my brother joined the army（why isn’t have passed?Maybe the key is wrong,I think）
baby knows that he should not take the things that do not beloong to him.为什么不可以是he,his,
is that a building?回答：yes,it is 为什么不是that is
what's it?it's an egg.为什么what‘it?不用this