搜题请搜索小程序“爱下问搜题”
问题 选择题

下列有关化学基本概念的判断依据正确的是（　　）

A．共价化合物：是否含有共价键

B．氧化还原反应：元素化合价是否变化

C．强弱电解质：溶液的导电能力大小

D．离子晶体：液态时能否导电

答案

A、含有共价键的化合物不一定为共价化合物离子化合物中也可能含有共价键，如NaOH，故A错误；

B、氧化还原反应的特征是有化合价的变化，可以根据元素化合价是否变化来确定是否是氧化还原反应，故B正确；

C、溶液的导电能力和电解质的强弱无关，根据电解质在水溶液中是否完全电离将电解质分为强电解质和弱电解质，故C错误；

D、离子晶体中含有离子键，液态时能否导电的不一定是离子晶体，如金属单质，故D错误．

故选B．

选择题

党的十八大报告确定的大会主题中提出：“为全面建成小康社会而奋斗”，这与十七大主题中“为夺取全面建设小康社会新胜利而奋斗”的表述不同。从“建设”到“建成”，一字之变，体现了我国发展阶段的重大变化。一词之变表明

①世界是物质的，意识对物质具有推动作用 ②主观与客观要做到具体的历史的统一

③真理在发展中不断超越自身            ④实践总要随着认识的变化而变化

A．①②

B．②③

C．③④

D．②④
查看答案
单项选择题

Scientists around the world are racing to learn how to rapidly diagnose, treat and stop the spread of a new, deadly disease. SARS — Severe Acute Respiratory Syndrome — was (1) for the first time in February 2003 in Hanoi, (2) since then has infected more than 1,600 people in 15 countries, killing 63. At this (3) , there are more questions than answers surrounding the disease.

Symptoms start (4) a fever over 100.4 degrees F, chills, headache or body (5) . Within a week, the patient has a dry cough, which might (6) to shortness of breath. In 10% to 200% of cases, patients require (7) ventilation to breathe. About 3.5% die from the disease. Symptoms (8) begin in two to seven days, but some reports suggest it (9) take as long as 10 days. Scientists are close to (10) a lab test to diagnose SARS. In the meantime, it is diagnosed by its symptoms. There is no evidence (11) antibiotics or anti-viral medicines help, (12) doctors can offer only supportive care. Patients with SARS are kept in isolation to reduce the risk of (13) . Scientists aren’t sure yet, but some researchers think it’s a (14) discovered coronavirus, the family of viruses that cause some common colds.

Most cases appear to have been passed (15) droplets expelled when infected patients cough or sneeze. Family members of infected people and medical workers who care for them have been most likely to (16) the illness. But recent developments in Hong Kong suggest that the (17) might spread through air, or that the virus might (18) for two to three hours on doorknobs or other (19) Health experts say it is (20) , though, that sharing an elevator briefly with an infected person would be enough to pass the virus.

2（）

A.but

B.and

C.or

D.yet
查看答案