我国最早的纸出现在[ ]
A.秦
B.西汉
C.东汉
D.五代十国
答案:B
Hundreds of students came to Shaoxing to work ____ the World Choir Games in 2010. [ ]
A. at
B. with
C. for
D. on
在某溶液中仅存在Na+、Fe3+、SO42-三种离子,已知Na+和SO42-个数比为3:2,则Na+、Fe3+和SO42-三种离子的个数比为( )
A.9:1:6
B.3:1:2
C.1:1:1
D.6:1:9