Kate loves music very much, and he is going to learn how to______.[ ]

A. keep healthy    

B. play an instrument

C. play basketball   

D.  listen to music

在吸收剂量的绝对刻度中，空气吸收剂量校准因子用如下哪一物理量表示（）

A.Km

B.Katt

C.N_x

D.N_k

E.N_D