Assuming that markets are efficient, which of the following statements is FALSE（）

A. Markets will not be volatile.

B. Investors should not trade often.

C. Investors should buy and hold passively managed index funds.

气动薄膜调节阀不动作，应（）

A、用万用表测试信号是否正常

B、看看风表压力够不够，检查气源

C、尝试手动动作阀门

D、尝试更换定位器