In modern world, most people have at least one time-telling tool with them, such as mobile phones, MP5 players and mini computers. Since these small machines are so common, will people stop wearing the 500-year-old watches? Maybe the answer is "yes", According to a survey, most teenagers say it's unnecessary to wear a watch, they usually use their mobile phones to tell the time.

 However, watchmakers say that watches will get popular again when people reach their 20s and 30s. By then, they want to spend money on a creative(有创意的) time-telling tool because they think it's not enough if a watch can just keep good time, so watchmakers are trying their best to create new kinds of watches. Recently, a new kind of watches has been invented. It can use different color lights to tell the time. This kind of watches makes people talk more about modern watches again.

 Also people want their time-telling tools to be beautiful, fashionable and practical(实用的), so watches are designed(设计) to meet the need of almost any personality(个性). Now more and more watches can be used as compasses(指南针), calendars and even USB drives …

 All in all, a watch has become more important than the time it tells. 

下列计算正确的是(       )

在“用天平和量筒测定固体密度”的实验中，某同学正确测得石块质量为48g，体积（如下图a）为____cm³，石块的密度是____kg/m³。图b是个别同学在实验操作过程中的情况；图c是部分同学实验结束离开实验室后留下的情景。指出图中违反实验操作规则的不规范之处。

图b：____；

图c：____。