特高压直流控制系统从功能上可以分为几层。（）
A.站控制层
B.双极控制层
C.极控制层
D.换流器控制层
参考答案：A, B, C, D
导游员在讲解时，既要如实地进行宣传，又要进行适度的夸张。 ( )
________ Barbara Jones offers to her fans is honesty and happiness.[ ]
A. Which
B. What
C. That
D. Whom
r fans is honesty and happiness.[ ]