Every time he tried to start the car，the wheels __________ deeper into the mud．

A.stayed

B.dropped

C.struck

D.sank

答案及解析： D

解析：

该题考查动词词义辨析.stay逗留；

drop使……落下；

strike打，袭击；

sink下沉.sink deep into the mud表示“深陷泥巴中”，答案为D.