Not until we have had a chance to discuss it thoroughly ________ perfectly.

A．the problem has been settled

B．has the problem been settled

C．will the problem be settled

D．the problem was settled

自然被动免疫中，可从母体获得的抗体类别是( )

A．IgG₁
B．sIgA
C．IgA
D．IgM
E．IgG₂