如图所示，将同一个物体分别沿AB和AC两个光滑斜面匀速拉到顶端。两次的拉力分别为F1和F2，两次做的功分别为W1和W2，则F1______F2, W1______W2。(两空都选填
在平面直角坐标系中,圆心O的坐标为(-3,4),以半径r在坐标平面内作圆, (1)当r____________时,圆O与坐标轴有1个交点; (2)当r____________时,圆O与坐标轴有2个交点; (3
常温下，下列各组微粒在指定的溶液中一定能大量共存的是( ) A．加入金属铝产生H2的溶液中：NH4+、Na＋、SO42-、CH3COO－ B．含有大量ClO－的溶液中：K＋
在试管中注入某红色溶液，给试管加热，溶液颜色逐渐变浅，则原溶液可能是( ) A．滴有酚酞的Na2CO3溶液 B．溶有SO2的品红溶液 C．滴有石蕊的AlCl3溶液 D
My friend Michelle is blind, but you’d never know it. She makes such good use of her other 21 , including her “sixth sense”, that she rarely gives the impression she’s 22 anyt
为防止硝酸厂产生的氮氧化物污染环境，通常用NaOH溶液吸收这些氮氧化物，反应的化学方程式为：NO+NOχ+2NaOH＝2NaNO2+H2O，方程式中χ时值是
下列各组离子在溶液中可以大量共存，且加入氨水后也不产生沉淀的是A. Na+、Ba2+、Cl-、SO42- B. K+、AlO2-、NO3-、OH-C. K+、NH4+、Al3+
. Nobody noticed the thief slip into the house because the lights happened to_________. A. go out B. give in C. turn off D. be put up
