The lady was so absorbed in her job that she didn't hear a customer at the door.A. to kn

问题补充：

The lady was so absorbed in her job that she didn hear a customer at the door.

A. to knock

B. knocking

C. be knocked

D. knocked

答案：

A. to knock

(答案→)B. knocking

C. be knocked

D. knocked

解析：答案：B考查非谓语动词。句意：这位女士如此专注于她的工作以至于她没有听到有位顾客正在敲门。hear sb. doing sth.听到某人正在做某事。