一口深井,井底有一只青蛙,这只青蛙白天沿着井壁向上爬3米,夜间又落下2米,到了第十天的下午,这只青蛙恰好爬到井口,则这口井的深度是( ).
12米
I went to Shanghai for several times and I ______ in love with it. [ ]
A. fall
B. feel
C. fell
D. felt
债的保证