A good teacher must be able to hold his students’ attention ____ he reaches the end of the class.

A．when

B．after

C．until

D．unless

外周血管痉挛性疾病可选用何种药治疗

A．山莨菪碱
B．异丙肾上腺素
C．间羟胺
D．普萘洛尔
E．酚妥拉明