GB5009.33-2010规定，用分光光度法测定速冻菠菜中的硝酸钠时，样品经沉淀蛋白质后，为了使硝酸根离子还原成亚硝酸根离子，可将溶液()。
A. 沉淀
B. 通过镉柱或加入镉粉
C. 过滤
D. 加入铁粉
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感官检定时，()对检验员的视力有一定的要求。
A. 气味
B. 杂质
C. 滋味
D. 组织状态
You may fly to Japan next Saturday,() you don't mind changing planes on the way.
A. as far as
B. unless
C. supposing
D. provided
My stomach hurts. I feel sick. —For safety's sake, ().
A. go to see a doctor tomorrow
Better to go to hospital
C. you'd better see a doctor at once
D. Quick go to hospital
Which of the sentences below best expresses the essential information in the highlighted sentence in paragraph 6？ Incorrect choices change the meaning in important ways or leave out essential information.
A. We see nature as precisely balanced because nature is unchanging.
B. A precise balance of nature is not possible because of the complexity of natural systems.
C. Our sense that nature is precisely balanced results from the illusion that it is unchanging.
D. Because nature is precisely balanced, complex systems do not seem to change.
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