—Is Jack in the classroom now? 

—No, he          football on the playground.

A．plays

B．played

C．is playing

D．was playing

强度高于40Mpa的芯样试件，宜用下列哪种材料对端面进行补平（）。

A.水泥砂浆

B.聚合物水泥砂浆

C.硫磺胶泥

D.环氧胶泥