与CD4结合的区域是指（）

A.α₁功能区

B.β₁功能区

C.α₁和β₁功能区

D.α₂和β₂功能区

E.β₂功能区

- Has John arrived yet?   

-- No, she _______ an hour ago.

A．was supposed to come

B．must have come

C．should come

D．ought to have come