许多孕妇都出现了维生素缺乏的症状，但这通常不是由于孕妇的饮食中缺乏维生素，而是由于腹内婴儿的生长使她们比其他人对维生素有更高的需求。 为了评价上述结论的确切程度，以下哪项操作最为重要
A．对某个不缺乏维生素的孕妇的日常饮食进行检测，确定其中维生素的含量。
B．对孕妇的科学食谱进行研究，以确定有利于孕妇摄入足量维生素的最佳选择。
C．对日常饮食中维生素足量的一个孕妇和一个非孕妇进行检测，并分别确定她们是否缺乏维生素。
D．对日常饮食中维生素不足量的一个孕妇和另一个非孕妇进行检测，并分别确定他们是否缺乏维生素。
E．对孕妇的科学食谱进行研究，以确定有利于孕妇摄入足量维生素的最佳选择。
参考答案：C
解析：该项意味着，孕妇缺乏维生素而非孕妇不缺乏维生素，则题干的结论就是对的；否则题干的结论就是错的。
If you are lost in the mountain, don’t get nervous. Staying calm will greatly your chances of survival. Many people think that good preparation is very . But actually the most important thing is to keep calm. In order to survive, you can do the following things. First, find a hiding place. Unnecessary movement will make you . You’d better find a hiding place to rest in order to save your . If you are in snow, you may be able to dig a cave for protection the cold weather. Second, send a signal(信号) to searchers for help. The best time to a signal for help is during the day. Do this from the point. It will be easier for searchers to see you. If you take a box of matches, build three smoky fires with some dry branches and the will tell other people where you are. Third, do not walk away. Walking away will make it more difficult to find you, searchers will try to follow your path and may you if you have gone off in a different direction. Searchers often find a car with no one in it.
|