化简求值:(4a2-2a-6)-2(2a2-2a-5),其中a=-1.
原式=4a2-2a-6-4a2+4a+10
=2a+4,
当a=-1时,原式=2×(-1)+4=2.
在人体实验中使用对照组、安慰剂和双盲法()
A.是人体实验的重要方法
B.是对病人的一种欺骗
C.是违背人道主义原则的
D.是违背知情同意原则的
E.会损害受试者利益
Which of the following statements about testing software with data is (are) true Ⅰ. The primary purpose of such testing is to find errors. Ⅱ. Such testing can demonstrate the existence of errors but cannot demonstrate the absence of errors.
A. Neither
B. I only
C.Ⅱonly
D.Ⅰand Ⅱ