A.1             B.2            C.3            D.

A.MN＞P                           B.MN≤P

C.MN≥P                            D.MN＜P

A.a²+b²+c²≥2                            B.(a+b+c)²≥3

C.++≥                      D.abc(a+b+c)≤

A.若AC与BD共面,则AD与BC共面

B.若AC与BD是异面直线,则AD与BC是异面直线

C.若AB=AC,DB=DC,则AD=BC

D.若AC=AC,DB=DC,则AD⊥BC

A.a²+b²+c²≥2                             B.(a+b+c)²≥3

C.≥2                       D.a+b+c≤