问题补充：
exciting sport it is to climb the mountains！
A. How
B. How an
C. What a
D. What an
答案：
A. How
B. How an
C. What a
(答案→)D. What an
解析：以what引导的感叹句的基本句型结构为what a/an +adj+可数名词单数+主语+谓语！；what+adj+可数名词的复数/不可数名词+主语+谓语！以how引导的感叹句的基本句型结构为how+adj/adv+主语+谓语！
