1.应该把medicine改成medical（因为此处要用形容词形式,medical care）
2.mosquitoes是可数名词,所以annoy应该保持不变.
3.应该把have改成having,因为前面有be动词are,所以后面的动词have应该变为having,sure在这儿是副词,表达“一定”的意思.
4.I enjoyed being with him when I was traveling.
5.The boy is very clever.He always comes up with good ideas.
希望能对你有些帮助.