Last year the number of students who graduated with a driving license reached 200,000, a (n)

________ of 40,000 per year. [ ]

A. average  

B. number

C. amount  

D. quantity

STIR技术的特点是：（）

A.信号抑制的选择性

B.扫描时间短

C.适用于增强扫描

D.大FOV扫描也能获得良好的脂肪抑制效果

E.对场强的依赖性很高