属于实质性器官的是
B
暂无解析
设函数f(x)=1-x^2在区间(,)
曲线的渐近线条数()
设数列{an}的前n项和为Sn，则{an}等差。
(1)Sn4=n2+2n,n=1,2,3
(2)Sn4=n2+2n+1,n=1,2,3
Edisontestedmorethanonethousandmaterialstoseeiftheycould_____electric;currentandglow.
Itisestimatedthat，currently,about50，000speciesbecome_____everyyear．
