A:I believe not
B:I might as well
C:It doesn't matter
D:I don't care
如果(x+m)与(x+3)的乘积中不含x的一次项,则m的值为( )
某人对着一口枯井大叫一声,经过0.2s后听到了回声,问这口枯井约有多深?