如图所示为某简谐运动的图象,若 时,质点正经过O点向b运动,则下列说法正确的是( )
He said he was very sorry because it was _______ his power to make the final decision. _______, I had to turn to others for help.
同体积的水和酒精混合后,____不变,____改变。
某金属单质跟一定浓度的硝酸反应,假定只产生单一的还原产物。当参加反应的单质与被还原的硝酸的物质的量之比为2∶1时,还原产物是( )