如图所示,球A在斜面上,被竖直挡板挡住而处于静止状态,关于球A所受的弹力,以下说法正确的是( )
蕨类植物的植株一般比苔藓植物高大的主要原因是( )。
——All the teachers went on a trip to Hainan yesterday Mr. White. Why?——Because he was too busy a new novel to travel.