It's time _____________ lunch.[ ]
A. have
B. to have
C. has
D. having
答案:B
阅读下文,寻找规律,并填空:
(1)已知x≠1,计算:(1-x)(1+x)=1-x2,(1-x)(1+x+x2)=1-x3,(1-x)(1+x+x2+x3)=1-x4,…
(2)观察上式,并猜想:(1-x)(1+x+x2+…+xn)=______.
有意识地选取了100亩小麦地来估算某县小麦总产,这种调查方式属于()。
A.重点调查
B.典型调查
C.抽样调查
D.都不对