对胎儿最安全的监测方法（）。

A.胎儿监护仪监测

B.胎心率监测

C.羊膜腔监测

D.胎儿头皮血血气分析

E.B超检查

--- Catherine, I have cleaned the room for you.

---Thanks. You _______ it. I could manage it myself.

A．needn’t do

B．needn’t have done

C．mustn’t do

D．shouldn’t have done