如右图所示,带有正电荷的A粒子和B粒子同时以同样大小的速度从宽度为d的有界匀强磁场的边界上的O点分别以30°和60°(与边界的夹角)射入磁场,又恰好都不从另一边界飞出,则下列说法中正确的是A.A、B两粒子在磁场中做圆周运动的半径之比是B.A、B两粒子在磁场中做圆周运动的半径之比是C.A、B两粒子的之比是D.A、B两粒子的之比是
We human beings should be very careful with what we do with nature, _____power is beyond our understanding.
()I found the lecture hard to follow because it ____ when I arrived.
I haven’t finished my report, but I promise I ______ it by the end of the week.
It's a custom in China to have some tea or other drinks before the meal ________.
—What’s all that noise about outside? —Oh, I forgot to tell you. The road to the railway station ______.