注意的基本特征是（）。    

A.指向性和集中性

B.计划性和集中性

C.指向性和逻辑性

D.逻辑性和计划性

E.综合性和抽象性

---I think Helen is at home.

---No, she    be at home, for she phoned me from the airport just five minutes ago.

A．mustn't

B．needn't

C．can't

D．dared not