已知|AB|＝2，动点P满足|PA|＝2|PB|，试建立恰当的直角坐标系，动点P的轨迹方程为____．

读音选词 根据所给句意和音标，从每题A、B、C、D四个选项中，选出一个最佳答案。
There will be heavy rain and strong wind next____. / wi:k /

How often do you exercise? I exercise ____ / wʌns/ a day.

The library is on the left____  /said / of the bank.

You'll ____ /feil/ in the final exam if you don't work harder.

If I had one million dollars, I'd give it away to ____ /′medikəl/ research.

多音字组词我最棒。

觉 jué____  jiào____       少  shǎo____  shào____

在光纤通讯中，电磁波的传播速度是____m/s，通讯用的激光从光导纤维的一端射入，在内壁上经过多次____（选填“反射”或“折射”），从另一端射出，从而把它携带的信息传到了远方．