He was too tired and fell asleep with a book open on his knee.A. layingB. lyingC. laidD. l

问题补充：

He was too tired and fell asleep with a book open on his knee.

A. laying

B. lying

C. laid

D. lain

答案：

A. laying

(答案→)B. lying

C. laid

D. lain

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