—He didn’t go to the lecture this morning, did he? —      . Though he was not feeling very well.

—You like listening to Sally’s songs, don’t you? —      . She has a sweet voice.

—It’s sunny today.Let’s go mountain climbing,      ?—Good idea!

Don’t forget to give Polly some food and change her water,       ?

John,clean your room,         ?

There is some important information in the newspaper,        ?

The town government set up a new modern hospital for the farmers,        ?

Your father used to eat meat,       ?

体积相同的实心球甲和乙由两种不同材料制成,在天平右盘中放两个甲球,左盘中放三个乙球时,天平恰好平衡,则()

甲物质的密度为,乙物质密度为,各取一定质量混合后密度为。假设混合前后总体积保持不变,则所取甲、乙两种物质的质量之比是()