生呕血的主要因素是
A.血小板减少
B.曲张静脉破裂出血
C.胃黏膜缺血及H+弥散进入黏膜
D.胃酸分泌增加
E.药物导致纤溶功能亢进
参考答案:C
The Science Museum, _____ we visited during a recent trip to Britain, is one of London@^@^@s tourist attractions. [ ]
A. which
B. what
C. that
D. where
直线回归分析中,对回归系数作假设检验,HO是()
A.β=0
B.ρ=0
C.μ=0
D.τ=0
E.M=0