(a-2b)2=______.
(a-2b)2=a2-4ab+4b2.
故本题答案为:a2-4ab+4b2.
—How is your sister now?
—______
A.She is thirty
B.She is a nurse
C.she’s much better
D.She’s Yang Jie
()即把所有调查对象都按某种标志排列起来,按一定顺序、时间抽取样本。
A.等距抽样
B.多级抽样
C.聚类抽样
D.随机抽样