He was working quietly with all his attention on the task.A. was fastenedB. fasteningC.

问题补充：

He was working quietly, with all his attention on the task.

A. was fastened

B. fastening

C. to fasten

D. fastened

答案：

A. was fastened

B. fastening

C. to fasten

(答案→)D. fastened

解析：可联系答.案.网客服索取。