Hundreds of students came to Shaoxing to work ________ the World Choir Games in 2010.
A:at
B:with
C:for
D:on
如果配制6%的氯化钠溶液的溶质质量分数偏小,其原因是( )
如图所示,要使杠杆处于平衡状态,在A点分别作用的四个力中,最小的是()
2x+x=( )