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
