They are singing----------.How ------they look.happy.happily
问题描述：
They are singing----------.How ------they look.happy.happily
答
They are singing happily.How happy they look.
他们正尽情得唱歌.他们看起来真高兴啊!
happily是副词,happy是形容词
前一句中,动词（sing）后面需用副词（happily）来修饰.
后一句中,look相当于系动词,后面接形容词（happy）