—Must he finish the work before lunch?
— ___________. He can do it in the afternoon.
A:Yes, he must.
B:No, he mustn't.
C:No, he needn't.
一个铜球的质量是178g,体积是40cm3,判断这个铜球是空心的还是实心的?如果是空心,则空心部分体积多大?如果给空心部分灌满水,则球的总质量是多大?(ρ铜="8." 9×103kg/m3)
设n∈-1,12,1,2,3,则使得f(x)=xn为奇函数,且在区间(0,+∞)上单调递减的n的个数是( )
根据课文连一连。