单项选择题
x是整型变量,下列选项中,与表达式not x< =1 and not x>6等价的是()①not(x< =1 and x>6)②not(x< =1 or x>6)③x>1 and x< =6④x>1 or x< =6
A.①③B.①④C.②③D.②④
A.9B.9.8C.4D.4.0
A.5B.1C.15D.25