题目

给出下列命题:①若a>b,则ac2>bc2;②若ab>c,则b>;③若-3a>2a,则a<0;④若a<b,则a-c<b-c,其中正确命题的序号是：                         (      )­  A．③④­B．①③­C．①②­D．②④ 答案：A解析:根据不等式的基本性质，可知若a>b,则ac2bc2，①错；ab>c，当时，b>，而题中未说明前提条件，②错；③④都是不等式性质的正确应用。故选AMSG(monosodium glutamate) is a food additive(食品添加剂),which has been widely used by many food factories all over the world since it appeared first in Japan in 1909. MSG is a substance that is added to some food to improve its original(原先的) taste and colour. It is used in foods around the world such as cakes, bread, frozen meats, fish and vegetables. In the beginning, people thought MSG was safe just like salt and sugar. However, in 1968 some people reported they seemed to have bad reactions(反应) to MSG after having had a meal at a restaurant. They included headaches and quick heartbeat(心跳).It was also reported that MSG excited a person’s brain and caused his death in Japan. Scientists think that MSG may lead to many neurological disorders(神经紊乱).In mice studies done by a university, the evidence showed the mice didn’t want to eat the food including MSG. Today many food companies “hide” MSG on food labels(标签) by using different names. If you see “natural flavorings”,“hydrolyzed protein”and “spices” in a food label, you are probably seeing a hidden way to “report” MSG in a food label. Every time we have a meal in a restaurant, we always feel the food very delicious to taste, but sometimes it is dangerous for our health because some poisonous food additives have been added to the food. To protect people’s health, our governments, from central to local, are taking actions to stop factories producing poisonous food additives.小题1: Monosodium Glutamate is _______A．a foodB．an additiveC．a factoryD．a country小题2:MSG is often used in ______.A．frozen meatsB．cupsC．clothesD．book covers小题3:The examples in the second paragraph tell us ________.A．the food including MSG is deliciousB．people like to eat in a restaurantC．mice like eating the food including MSGD．MSG is not safe sometimes小题4:If you see “natural flavorings”,“hydrolyzed protein” and “spices” in a food label, you will know ­­­­­­­_____________.A．you must eat the food in a hidden wayB．the food label must be hiddenC．MSG is probably added to the foodD．you must report the food to your parents小题5:The underlined word “substance” in the article means __________.A．colourB．materialC．tasteD．food