A：ought to joi
B：should have joined
C：would rather not have joined
D：would like to have joined
在一对相对性状的遗传实验中，性状分离是指 ( )
观察下列各式
（x﹣1）（x+1）=x2﹣1
（x﹣1）（x2+x+1）=x3﹣1
（x﹣1）（x3+x2+x+1）=x4﹣1
根据规律可得（x﹣1）（xn﹣1+…+x+1）=____（其中n为正整数）
