It is great fun为什么不加冠词?为什么a heavy rain加冠词?都是不可数名词,为什么一个加一个不加?

It is great fun为什么不加冠词?为什么a heavy rain加冠词?都是不可数名词,为什么一个加一个不加? what great fun it is to go hiking!为什么因为fun是不可数名词不加a,而不说它抽象名词具体化呢?还是因为fun不属于抽象名词具体化的范畴? reading is fun 为什么fun不加ly? What great fun it was!fun前可不可以加a?为什么? What great fun it was! fun前可不可以加a?为什么? In my opinion ,collecting stamps is a great fun for me 不加那个a吧 可是为什么 It is fun to have ice cream in summerice cream前为什么不加an 为什么what great fun it is 这个句子里,great前没有a? what great fun it is to go hiking in such fine weather!和what a great fun .!哪个对?为什么? it is great fun后应加什么时态 It is great fun啥意思? You can't be image_________ great fun chatting online is.答案是what ,请问为什么不能用how great fun? what a great fun/what great fun为什么不可以用how great fun __ it is to play with snow in winter!A How fun B what a fun C How great fun D what great funA 不行吗 How+adj 英语it is to jump into a river in summer!A how fun B how funny C what great fun D what a great fun为什么 为什么是what great fun it is!而不是what a great fun it is! it is a great fun to do sth.还是it is great fun to do sth what great fun it is to go camping in such fine weather,为什么不说what a great fun it is to gocamping in such a fine weather?