---Bob looks upset. What has happened to him?

---Perhaps his failure to the exam___ his low spirits.

A．accounts for

B．looks for

C．makes for

D．takes for

生态影响预测评价方法中，指数法的应用包括( )。

A．生态因子单因子质量评价

B．生态系统功能评价

C．生态多因子综合质量评价

D．进行生态影响的定性分析与评价