腭裂是由于

A．侧腭突和前腭突融合障碍

B．上颌突和侧腭突融合障碍

C．侧腭突和鼻中隔融合障碍

D．侧腭突和继发腭融合障碍

E．侧腭突和球状突融合障碍

If two events can not both occur in a single trial, they are ______ .

A．false events

B．mutually exclusive

C．statistically independent

D．just in time