1.keep
keep doing sth 结构
2.sports(常用复数),likes(动词第三人称单数)
3.B 此处非过去式,只是动词的过去分词演变而成的表状态形容词,有修饰作用,意为“关着的”
4.C
主语：most of the students
谓语：exercise
in our class:介词短语作地点状语后置
after school 时间状语
to keep healthy：目的状语
整句意思为：我们班上大多数学生,为了有健康的身体,课后锻炼.
5.a little worried “有点担心” a little + 形容词 ,表示程度轻微
6.to study/learn
help sb.to do sth 结构
7.Eating,healthy
8.do ,like
like sb.to do sth.,等同于want sb.to do sth.意思即为想要某人做某事