I don’t think she noticed the headmaster just at that moment, for she _______ the game on her cellphone.

A．played

B．was playing

C．is playing

D．has been playing

阳离子聚合物钻井液中的大阳离子，其主要作用是（）钻屑而使其沉除。

A、抑制

B、水化

C、分散

D、絮凝