In the past few years, research has suggested that Vitamin D may increase the level of serotonin（血清素）, one of the key nurotransmitters influencing our mood, and ________it helps to relieve mood disorders. 

A．that

B．where

C．what

D．which

模块独立性是软件模块化所提出的要求，衡量模块独立性的度量标准是模块的( )

A．抽象和信息隐蔽

B．局部化和封装化

C．内聚性和耦合性

D．激活机制和控制方法