什么是规范汉字？
参考答案：
规范汉字是指经过整理简化并由国家以字表形式正式公布的正体字、简化字和未经整理简化的传承字。
You ________ in person; a telephone would have been enough.
A．couldn't have come
B．needn't have come
C．shouldn't have come
D．mustn't have come
总体为正态分布，δ2未知，估计总体均值置信区间的统计量是（）。
A.A
B.B
C.C
D.D
