只要我们细心观察，在我们的身边，随处可见令人痛心的浪费现象，如浪费粮食、学习用品、教学器材 等。其实，我们丢掉的不仅仅是“东西”，我们丢掉 的可能是我们的“心”，一颗高尚的心，一颗能让我 们生活幸福的心。在生活水平不断提高的今天，我们依然提倡勤俭节约的优良作风的原因是（    ）

①资源和财物总是有限的，不能肆意挥霍                                                ②我国人均资源占有量很少

③我国目前还处于社会主义初级阶段，还有很多人的生活并不富裕    ④所有的用品都是通过劳动者辛勤劳动生产出来的，来之不易

为了研究早餐质量对学生血糖和胰岛素水平的影响，某研究小组选取40名健康学生志愿者，按平时早餐习惯分成不进早餐组、高糖组、高脂高蛋白组和均衡营养组，按组别给予相应早餐，并分别于空腹（餐前）和餐后1、2、3小时取静脉血检测血糖浓度和胰岛素含量，实验期间不食用其他食物，实验结果如图．请回答下列问题：

如图甲所示是某型号的浴室防雾镜，其背面粘贴有等大的电热膜。使用时，镜面受热，水蒸气无法凝结其上，便于成像，下表是该防雾镜的相关数据：

在DNA 测序工作中，需要将某些限制性内切酶的限制位点在 DNA上定位，使其成为 DNA 分子中的物理参照点。这项工作叫做“限制酶图谱的构建”。假设有以下一项实验：用限制酶 HindⅢ，BamHⅠ和二者的混合物分别降解一个 4kb（1kb即1千个碱基对）大小的线性DNA 分子，降解产物分别进行凝胶电泳，在电场的作用下，降解产物分开，如下图所示。

据此分析，这两种限制性内切酶在该DNA 分子上的限制位点数目是以下哪一组？（ ）

根据短文理解，选择正确答案。

    Winter-swimming has become popular in Beijing. Three years ago, few people would go swimming in the city waters. But now there is a Winter-swimming Enthusiasts' Club(冬泳爱好者协会)and it has more than 2,000 members. The oldest is 84 years of age and the youngest is only 7. The members are from all ways of life__They may be workers, peasants, soldiers, teachers, students...

    Though it is now the coldest part of the season and the water temperature in the city's lakes is around 0°C, many winter-swimmers still swim in the icy waters, even when it is snowing. They enjoy themselves in the lake, while the people by the side of the lake are wearing heavy clothes.

    Why are so many people interested in winter-swimming? Because winter-swimming can be good for one's health.

    Bei Sha is a good example. He is 69 years old, and he once suffered from heart trouble for 26 years. After ten years of winter-swimming he is now in good health.

    Scientists are now studying the effects of winter-swimming on health.