Linda          sleep late, but now she          getting up early to catch the bus.

A．used to; is used for

B．used to; is used to

C．is used to; is used for

D．is used to; is used to

预应力混凝土大直径管桩（大管桩）采用离心、振动、辊压复合工艺生产高强度混凝土管节，生产时预留穿筋孔道，然后对拼接的若干管节穿筋张拉施加后张预应力，使之拼成长桩。施加于混凝土的有效预压应力为（）左右。

A.2～4MPa

B.4～6MPa

C.6～12MPa

D.15MPa