Betty goes to learn how to play the violin every afternoon _____ Saturday and Sunday.

She does the housework on these days.[ ]

A. on

B. during

C. except

D. from

通过花冠的中心能切出两个以上对称面的花冠称为（）。

A.不整齐花冠

B.整齐花冠

C.两侧对称花冠