缺乏后可使服用洋地黄的患者发生心律失常的元素是（）。
A.钠
B.钙
C.锌
D.钾
E.镁
参考答案：E
解析：镁是维持机体正常所必需的矿物质之一，也是很多生化代谢过程中一个必不可少的元素，其中最重要的是参与体内能量代谢中腺苷二磷酸与腺苷三磷酸之间一系列磷酸化和脱磷酸的往复逆转反应，从而维护中枢神经系统的结构和功能，抑制神经、肌肉传导的兴奋性，保障心肌的正常收缩、冠状动脉的弹力和反映调节酶的活力，参与各种酶的反应以及保存组织内的钾离子等。1978年有人证明，镁缺乏是心脏病发作的主要原因，其根据是当心脏病发作时血镁最低，随着症状的消失镁也恢复正常。
| 完形填空。 Scientists are trying to make the desert into good land again. They want to bring 1 to the desert, so people can live and grow food. They are 2 a lot about the desert. But 3 of the earth is becoming desert all the time, scientists may not be able to 4 . the deserts. Scientists think that people make deserts. People are doing 5 things to the earth. Some places on the earth don't get 6 . But they still don't become deserts. This is _7 _ some green plants are growing there. Small green plants and grass are very 8 to dry places. Plants don't let the wind blow the earth away. When 9 _ bit of rain falls, the plants hold the water. 10 plants, the land can become a desert much more easily. | |||
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