Phrase structure rules allow us to better understand ______.
A、how words and phrases form sentences
B、what constitutes the grammaticality of strings of words
C、how people produce and recognize possible sentences
D、All of the above
【正确答案】：D
【题目解析】：Phrase structure rules allow us to better understand how words and phrases form sentences, what constitutes the grammaticality of strings of words，and how people produce and recognize possible sentences.