收集所有质量可靠的随机对照试验经过荟萃分析属于（）
A．一级证据
B．二级证据
C．三级证据
D．四级证据
E．五级证据
参考答案：A
求函数y=log2(x2-6x+5)的定义域和值域．
Thomas Hardy's novels are said to suffer from the "long arm of coincidence" because too many events seem to have a casual rather than a （） connection.
A．incidental
B．substantial
C．causal
D．plausible
