【简答题】胃肠道平滑肌的紧张性和自动节律性主要依赖于()。
【单选题】Why does an astronaut put his hand under his belt when he sleeps?
A.
Because he thinks it is comfortable to sleep in that way in space.
B.
Because he doesn't want to touch any controls when he sleeps.
C.
Because the instruments of the spaceship are easily broken.
D.
Because he is afraid that the seat will move.
【简答题】如图所示,在△ABC中,∠C=90°,BD平分∠ABC交AC于点D,过点D作DE ∥ BC交AB于点E,过点D作DF⊥AB于点F,请回答下列问题. (1)DE与BE相等吗?请说明理由; (2)判断BC,DE,EF三者的数量关系,并说明理由; (3)平行线DE,BC之间的距离与DF的长度有何数量关系,为什么?
【单选题】温室效应会导致全球气候变暖,其主要原因是
A.
CO 2 增多使太阳辐射到地球表面的能量增多
D.
CO 2 、CH 4 等温室气体会吸收地球表面发出的长波辐射,减少地球的热量散失
【简答题】在△ABC中,∠ACB=90°,AC=BC,直线MN经过点C,且AD⊥MN于点D,BE⊥MN于点E.(1)当直线MN绕点C旋转到如图1的位置时, ①通过观察、猜想,△ADC和△CEB的关系是: ; ②猜想DE、AD、BE三者之间满足的数量关系是: ; ③请证明你的上述两个猜想. (2)当直线MN绕着点C顺时针旋转到MN与AB相交于点F(AF>BF)的位置(如图2所示)时,请直接写出下列问题的答案:...