确定混凝土配合比的主要参数有（）
A.水灰比
B.砂石比
C.单位用水量
D.骨料粒径
E.石子级配
参考答案：A, B, C
John and I＿＿＿friends for eight years.We first got to know each other at a Christmas party.But we＿＿＿＿＿ each other a couple of times before that.
A．had been； have met
B．have been； have met
C．had been； had met
D．have been； had met
电火花成型加工的主要工艺参数有哪些？
