沉淀免疫复合物所用PEC6000浓度为（）
A.3％～4％
B.6％～7％
C.8％～12％
D.12％～15％
E.25％
参考答案：A
Paul started hiking in 2010 and he has hiked across 11 countries ______.
[ ]
A. ever since
B. from then on
C. right away
D. at once
范蠡从商主张（）
A.不求暴力
B.大理推销
C.出奇制胜
D.趁火打劫
