计算加权综合指数时,帕氏指数将同度量因素固定在()期;而拉氏指数则固定在()期。
参考答案:报告;基
The students each _______________their own e-mail address.
A.has
B. having
C.have
D.has had
螺旋离心分离机工作原理、特点?