题目

The Olympics          in China in 2008.    A. has taken place     B. took place     C. has happened      D. happened 答案：B常温常压下，对密度公式ρ= m/V的理解，下列说法中正确的是 A．同种物质，密度跟质量成正比            B．同种物质，密度跟体积成反比 C．同种物质，密度跟质量和体积无关         D．不同物质，体积跟密度成反比