根据下列句子及所给汉语注释，写出空缺处各单词的正确形式，每空只写一词。
1. You should __________ (覆盖) the food with the cloth, or it will get dirty.
2. It’s reported that three _________(猴子) escaped from the local zoo last Friday.
3. I asked him to leave, but he ________(拒绝), so he still stayed there.
4.The boy _______ (伤) his leg while he was playing football.
5. The math problem is too difficult for me to work out _______(容易).