327-412+8
=3-22+22
=3.
故答案为:3.
命题“∃x∈R,x2-2x+4>0”的否定为______.
主要经粪-口途径传播的肝炎病毒是()
A.HAV和HBV
B.HCV和HAV
C.HDV和HEV
D.HAV和HEV
E.HCV和HEV