题目内容：

the [ ]children are singing english songs.the children are singing english songs[ ].the children
are singinf english songs because of their[ ].《happy》

优质解答

the [ happy]children are singing english songs.the children are singing english songs[happily ].the children are singing english songs because of their[ happiness].

追问：

最后一个我不明白

追答：

孩子在英文歌因为他们很幸福。 happiness做名词讲，表示“幸福”的意思.

追答：

1.development 名词形式 2.developed 发达国家 3.develops 第三人称单数 4.developing 发展中国家