— Why not work them out all by _____________?
A:themselves
B:himself
C:ourselves
D:myself
12÷3=4,表示把____个东西,每____个一份,分成了____份。
—Yes, when we cross the street we must wait ________ the traffic lights turn green.
已知数列an的a1=1,且an+1an=1-nan+1,则此数列an的通项公式为( )