—I lost touch with my teachers after I graduated from high schoo1.
—I still my teachers from high schoo1.
A:catch up with
B:keep up with
C:keep in touch with
已知向量a→=3,1,b→=x,-2,c→=0,2,若a→⊥b→-c→,则实数x的值为( )
在“植物﹣蝗虫﹣大山雀”这条食物链的分析中,描述正确的是( )
①测电阻前要使红、黑表笔相接,调节调零电阻,使表头指示电流为零;
②红表笔与表内电池正极相连,黑表笔与表内电池负极相连;
③红表笔与表内电池负极相连,黑表笔与表内电池正极相连;
④测电阻时,表针偏转角度越大,待测电阻阻值越大;
⑤测电阻时,表针偏转角度越大,待测电阻阻值越小.