(
)There isn't much clean water on the Earth. We should
it wisely.
A.used
B.useful
C.use
D.using
空处所在句缺少谓语动词，情态动词should后接动词时应用原形。故选C。
答案：C
解析：
本题考查情态动词should的用法，情态动词should后必须接动词原形。选项A是动词过去式，选项B是形容词，选项D是动词现在分词，只有C是动词原形，符合语法规则。
[反馈练习]（一）按要求完成句子。
1. They should colour the Earth in the picture.（改为否定句）
They
shouldn't
colour
the Earth in the picture.
2. She should arrive there before noon.（改为一般疑问句）
Should
she
arrive
there before noon?
3. We should
use glass bottles in our daily life.（对画线部分提问）
What
should
you
do
in your daily life?
答案：1. shouldn't colour
2. Should she arrive
3. What should, do
（二）用所给词的适当形式填空。
1. Sir, you shouldn't
smoke
(smoke) in the hospital.
2. What should
she
(she) do
to make
(make) good use of her talent(天赋)?
3. Bill, you should
use
(use) your money wisely, or you'll regret it.
4. Why should
children
(child) have a regular inspection(定期检查) every term?
答案：1. smoke
2. she, to make
3. use
4. children
