下列物质中,由分子构成的是( )
A:硫酸铜
B:金刚石
C:水
D:氢氧化钠
-________ do you think of your school life?
-It's very exciting (令人兴奋的).
While they ____(discuss) how to prevent accident, another accident happened.
下列句子中划线的成语使用正确的一项是 ( )