15×27×2=____
把肯定句改成否定句
①我班被评为先进集体,全班同学都感到自豪。
②今天他可能会来。
– Mum, I've been studying English since 8 o'clock. _____ I go out and play with Tom for a while?– No, I'm afraid not. Besides, it's raining outside now.
甲、乙两物体质量之比是1:2,体积之比是4:1,同时从同一高度自由下落,则下落加速度之比和下落时间之比分别为( )