what fun it is to listen music 这里的fun为什么不能是形容词用how fun.

what fun it is to listen music 这里的fun为什么不能是形容词用how fun. ----------it is to listen to music A How fun B How a fun C W What fun it is to listen to music in bed on rainy days.为什么to What fun it is to play .这里的what为什么不能用how? 为什么能说What fun it is to do sth.却不能说How fun it is to do sth. 为什么是what fun it is to. what fun it is to swim 为什么不能用how? how fun it is to do … what fun it is to do… 为什么要用后者,fun如果当形容 ( ) great fun it must be to go abroad!这里的fun是名词还是形容词? 为什么是what fun it is to.而不是how funn it is to. What -----fun it is to have a picinc in a park!这里的fun 是做名词还是 what fun day it is?为什么用fun,不用funny