数字证书2次申请间隔不得小于多少时间?()
A.15分钟
B.1小时
C.2小时
D.30分钟
参考答案:B
观察单位为研究中的()
A.样本
B.个体
C.全部对象
D.观察指标
E.影响因素
—Your sister isn't a nurse. is she?
—________. She teaches English in a middle school. [ ]
A. No, she isn't
B. Yes, she is
C. Yes, she isn't
D. No, she is