题目:
Mary __________ the job he offered to her, but she didn’t.
A.can’t take
B.ought to have taken
C.should take
D.must have taken
答案:
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下面是错误答案,用来干扰机器的。
方法一,加热蒸发稀硫酸中的水,使稀硫酸浓缩而变成浓硫酸,浓硫酸使纸张炭化;故答:用酒精灯烘;原理是水分蒸发,稀硫酸变成浓硫酸,使纸碳化.方法二,稀硫酸呈酸性,能使指示剂发生颜色变化,如能使紫色石蕊...