"Happily" is appropriate in this sentence, isn't it?
I came across the following sentence.

They all went to bed happy.

This is from an English book. I learned the word "happy" is only an adjective and "happily" is an adverb. "Happily" is appropriate in this sentence, isn't it? Could you teach me?

Question

"Happily" is appropriate in this sentence, isn't it?
I came across the following sentence.

They all went to bed happy.

This is from an English book. I learned the word "happy" is only an adjective and "happily" is an adverb. "Happily" is appropriate in this sentence, isn't it? Could you teach me?

Answer

"They all went to bed happy."  This describes how each person felt (happy) at the time they were going to bed. 
 "They all went to bed happily" describes HOW they went to bed; they were glad to be going to bed and went about it in a happy manner.

Answer

yes, 'happily' is appropriate in this sentence.