直流控制系统的故障等级有（）。
A.一般
B.轻微
C.严重
D.紧急
参考答案：B, C, D
. In the interview, he had finally ______ several customers of the advantages of his product
A．convinced
B．reminded
C．accused
D．informed
钻石颜色分级主要采用（）法对钻石颜色进行划分。
A.肉眼观察
B.仪器测定
C.比色
D.估算
