已知a+1a=5,求a4+a2+1a2的值.
读单词,选择画线部分发音不一致的选项。
① ____ A. think B. tooth C. with D. three
② ____ A. word B. short C. horse D. north
③ ____ A. bear B. pear C. wear D. year
④ ____ A. shout B. enough C. loud D. house
⑤____ A. win B. life C. bike D. time
一物体从楼上自由下落,经过高为2m的窗户所用的时间为0.2s,物体是从距离窗顶多高处自由落下的?