已知，， 和的夹角为，以，为邻边作平行四边形，则该四边形的面积为 .
（12分）下表是一辆电动自行车的部分技术指标，其中额定车速是指电动车满载情况下在平直道路上以额定功率匀速行驶的速度。 额定 车速 质量载重电
下列物质与水混合后静置，不出现分层的是A．乙酸 B．三氯甲烷 C．苯 D．四氯化碳
One day, a man found the cocoon (茧) of a butterfly and he brought it home.A few days later, the man saw a small hole in the cocoon. He sat and watched for several hours as a butterfly struggled to f
名著阅读。（4分）A却转过屋后山边来净手，只见一个汉子蹑手蹑脚从山后归来。A转过屋后听时，那妇人正要上山讨菜，开后门，见了，便问道：“大
This medicine will give you some r .
A、B、C、D、E都是短周期元素，原子序数依次增大，A、B处于同一周期，C、D、E同处另一周期。C、B可按原子个数比2∶l和1∶1分别形成两种离子化合物甲
Youth volunteers from Beijing university visited Song tang hospital, a care clinic for the aged and dying patients, during the second global youth service day on April 21． Thirty student volunteers
