—Jack is not in the office at the moment

—Oh, he ______ those who are going to take the driving test in an hour.

A．can have instructed

B．must have instructed

C．must be instructing

D．will be instructing

下述选项中，不是二尖瓣关闭不全体征的是（）

A.心尖区全收缩期高调吹风样杂音

B.杂音向左腋下或背部传导

C.第一心音增强

D.常有第二心音分裂

E.重度关闭不全时可出现心尖部舒张中期杂音