A:30°S,30°W
B:30°S,60°E
C:30°N,30°W
D:30°S,30°E
如图所示,弹簧所受重力不计,上端固定在天花板上,下端挂一个 小球,处于静止状态。下列各组力中属于平衡力的是( )
Results of not enough sleep
harm your problem-solving ____
____ your heart
lead to ____sleepiness
Ways to get better sleep
limit wine drinking ____ to bedtime
get ____ minutes of sunlight
读我国某类自然灾害出现频次图,完成下列问题。