地跨南北两半球,人口又在1亿以上的国家有( )
A.尼日利亚
B.巴基斯坦
C.印度尼西亚
D.孟加拉国
答案:C
等差数列{an}的前n项和为Sn,且9a1,3a2,a3成等比数列.若a1=3,则S4=( )
A.7
B.8
C.12
D.16
The number of the employees has grown from 1,000 to 1,200.This means it has risen ________ 20 percent.
A.at
B.by
C.to
D.with