— People should spare no efforts to protect the environment.

— ________. Air pollution does harm to our health.

A．All right

B．Take it easy

C．Go ahead

D．Exactly

MRI成像基础是（）

A.组织间吸收系数的差别

B.组织间密度高低的差别

C.组织间形态的差别

D.组织间质子密度和弛豫时间的差别

E.组织间大小的差别