蜗牛爬行时会留下痕迹,主要是由于什么器官分泌的黏液( )
A:壳
B:眼
C:触角
D:足
— Does he finish the picture?
— No. He _______ needs more time.
—What are those?
—They're ducks.
下列各句中,没有语病的一项是( )