软件维护是用户使用软件期间对其所进行的补充、修改和增强。可分为4类：完善性维护、校正性维护、适应性维护和______。

--- What sport do you like best?

--- Springboard diving (跳板跳水). _____ to dive into water from a high board!

A．What a fun is it

B．How fun it is

C．How a fun is it

D．What fun it is