下列结论一定正确的是( )
A:两数的差一定小于被减数
B:互为相反数两数差为0
C:一个数减去0的结果为0
D:0减去一个有理数的结果是这个有理数的相反数
They ________ carefully, but they didn't ________ anything.
椭圆x234+y2n2=1和双曲线x2n2-y216=1有相同的焦点,则实数n的值是 ( )