一道语法题

Lois6669

The major areas of medicine in which lasers are effective is in the cutting and closing of  blood vessels, and in the destruction of tumors.    
(A) is in the cutting and closing of blood vessels, and in the destruction    
(B) are the cutting and closing of blood vessels, and also the case of destroying    
(C) are the cutting, closing of blood vessels, and in the destroying    
(D) are the cutting and closing of blood vessels, and the destruction    
(E) is in the cutting and closing of blood vessels, and the destroying

选A 为什么是用IS ？不是the major areas吗？

Lois6669

是D

毛毛carina

这题是选D吧~~~