—Can those at the back of the classroom hear me?—No problem sir !A. seatB. seatingC. sea

问题补充：

—Can those at the back of the classroom hear me?—No problem, sir !

A. seat

B. seating

C. seated

D. sit

答案：

A. seat

B. seating

(答案→)C. seated

D. sit

解析：句意：那些坐在后面的（同学）能听到我吗？这里需要定语修饰those，而be seated“就坐”，也可以理解为是形容词的用法，意为“座着的”强调一种状态，而sit强调动作，应该用sitting，因此seated更合适，选C。