北方地区的农业特点是 ( )
A:农田多为旱地,作物一年三熟
B:农田多为旱地,作物一年一熟或两年三熟
C:农田多为水田,作物一年两至三熟
D:农田多为水田,作物一年三熟
先化简,再求值:xx2-1÷1+1x-1,其中x=3-1.
The French book must belong to _______, because he studies French.