Jack was once quiet in class,but now he becomes _____ and often answers questions.
根据本题语境可知，杰克以前在课堂上很安静，但现在他变得很活跃，经常回答问题。故所缺的词是 active。
He will _____ his diet because of his serious stomach problem.
四个选项的含义分别是：look forward to 期待；take pride in 为…而自豪；deal with 应对，处理；pay attention to 注意，关注。根据本题语境可知，他因为严重的胃病将会关注饮食，故答案选D。
根据句意及所给单词的汉语提示写出所缺的单词。
1.The(速度) of the fastest train in China is over 350kph.
2.I want to find a(搭档） to practice English with.
3.The number of the students has(增加）since last year.
4.We all think that he is a(天生的）singer.
5.Natural resources are very important for us and we should use them(明智的）.