—________ does your father play tennis after work?

—Every Tuesday and Thursday.

A．How often

B．How soon

C．Where

D．Why

仅由角质形成细胞合成的胶原是（）

A.Ⅶ型胶原

B.Ⅳ型胶原

C.Ⅻ型胶原

D.Ⅵ型胶原

E.Ⅹ型胶原