有区别.
第二句是指那些 words 的唯一的正确格式,
而第一句意味那些 words 有数个不同的正确格式.
用哪个要看句意的需求.
例句：
The right form of expressing sympathy to someone is to say "I'm so sorry to hear that".
The right forms of greeting someone you meet on the street are:
Good morning!
How are you?
Hello!
How's it going?