给定一个自然语言句子，请将其分解成语法结构。


I am reading a book.
Sentence: I am reading a book.

Syntax Tree:
            
                  (S)
                 /   \
               (NP)  (VP)
               /     /   \
              I     am   reading a book
                     /        \
                  (V)         (NP)
                  /           /   \
               reading       a   book
                                  |
                                  (N)
                                  |
                                 book