“千里之行,始于足下”这句名言告诉我们:培养和锻炼意志要 ( )
A:有明确的目标和计划
B:在艰苦的环境中锻炼
C:从细微之处做起,从小事做起
D:善于管理自己
—Tell me something about your adventure in the rainforest, please.
— We lost our way in the forest and ___ made matters worse was ___ night began to fall.
搬运工人用如图所示的滑轮组将一个重120N的物体匀速提升3m,所用的拉力为50N,不计绳重及摩擦.求:
①滑轮组的机械效率;
②动滑轮的重;
③若用该滑轮组同时拉4个这样的物体,拉力为多大.
北京天安门广场每天早晨升国旗时刻与日出同时,下列节日中,升旗时刻最早的是( )