A.0
B.∞
C.f(0,0)
D.1
[单选题]A.0B.∞C.f(0,0)D.1
[判断题]A.对B.错
[单选题]A.B.C.D.E.
[单选题]A.30B.40C.50D.20E.15
[单选题]A.B.C.D.