_____ like doing things [ ]
A. We both; the same
B. Both we; the same
C. We both; same
答案:A
设a1、d为实数,若首项为a1,公差为d的等差数列{an}的前n项的和为Sn,满足S5•S6=-15,则a1的取值范围是______.
散装液体化学品的直接接触毒害性常用()衡量。
A.LD50
B.EEL
C.LC50
D.A或C