生菜腐烂病在结球叶表面2～3层叶上产生（）病斑。
A.脓状
B.水渍状
C.灰黑色
D.褐色
参考答案：B
Mark Twin wrote many popular novels in his life, ________ The Adventures of Tom Sawyer is a best example.
A．of which
B．what
C．whose
D．which
