题目

下列关于元素周期律和元素周期表的论述中正确的是( ) A．同主族元素从上到下单质熔点逐渐升高 B．元素周期表是元素周期律的具体表现形式 C．同周期从左到右，元素原子半径逐渐增大 D．非金属元素的最高正化合价等于它的负化合价的绝对值 答案：解析：A项，碱金属元素从上到下单质熔点逐渐降低；C项，同周期从左到右，元素的原子半径逐渐减小；D项，第ⅣA族元素的最高正化合价才等于它的负化合价的绝对值。 答案：B用must, have to, can, ought to, need, should的适当形式填空。【1】You ________ keep your promise.【2】In some parts of the world, you ________ boil the water before drinking it.【3】He ________ stayed at home this morning. I saw him shopping in another city.【4】You ________ smoke in this part of the hospital.【5】You ________ keep a simple first aid box at home for any accidents.【6】You ________ take care of yourself when I’m away.【7】—You ________ have finished the article. The deadline is last Friday.—Sorry. I have been busy these days. Could you give me 3 days more?【8】He ________ have caught a bad cold last night, for his forehead felt burning.【9】You ________ walk so fast; we have enough time to catch the early train.【10】—Need I do that right now?—Yes, you ________.