great fun it is to have a trip to the park !AHowBWhatC. How aD. What a

问题补充：

great fun it is to have a trip to the park !

AHow

BWhat

C. How a

D. What a

答案：

A. How

(答案→)B. What

C. How a

D. What a

解析：此题重点考查感叹句的结构。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！

此句的中心词是fun是个名词，故感叹句的引导词是what，fun是不可数名词故what的后面不能加不定冠词，故选B。