问题 选择题

下列有关同分异构体数目的叙述不正确的是(  )

A.甲苯苯环上的一个氢原子被含3个碳原子的烷基取代,所得产物有3种

B.与

互为同分异构体的芳香族化合物有5种

C.含有5个碳原子的某饱和链烃,其一氯取代物可能只有3种

D.菲的结构简式为

,它与硝酸反应,可生成5种一硝基取代物

答案

A、甲苯苯环上有3种H原子,含3个碳原子的烷基有正丙基、异丙基两种,所以甲苯苯环上的一个氢原子被含3个碳原子的烷基取代有3×2=6产物,故A错误;

B、

分子式为C7H8O,所以芳香族化合物有如下五种异构体:

,故B正确;

C、有5个碳原子的某饱和链烃为C5H12,有正戊烷、异戊烷、新戊烷三种,正戊烷有3中H原子,一氯代物有3种;异戊烷有4种H原子,一氯代物有4种;新戊烷有1种H原子,一氯代物有1种,故C正确;

D、

为对称结构,有如图所示的5种H原子

,所以与硝酸反应,可生成5种一硝基取代物,故D正确.

故选A.

选择题
单项选择题

The earliest evidence of standardized testing based on merit comes from China during the Han dynasty. The concept of a state ruled by men of ability and virtue was an outgrowth of Confucian philosophy. Standardized testing has not traditionally been a part of European pedagogy. Based on the skeptical and open-ended tradition of debate inherited from Ancient Greece, Western academia favored the essay. The use of standardized testing in the United States is a 20th century phenomenon with its origins in World War I.

One of the main advantages of standardized testing is that the results can be empirically documented ; therefore the test scores can be shown to have a relative degree of validity and reliability, as well as results which are generalizable and replicable. This is often contrasted with grades on a school transcript, which are assigned by individual teachers. Another advantage is aggregation. A well designed standardized test provides an assessment of an individual’s mastery of a domain of knowledge or skill which at some level of aggregation will provide useful information.

Though many educators recognize that standardized tests have a place in tools used to assess student achievement, critics feel that overuse and misuse of these tests is having serious negative consequences on teaching and learning. The temptation is to use the tests to define curriculum and focus instruction. What is not tested is not taught, and how the subject is tested becomes a model for how to teach the subject. Moreover, standardized test scores are problematic tools for school accountability because the examinee scores are influenced by three things: what kids learn in school, what kids learn outside of school, and innate intelligence. Critics believe this is not possible. While it is possible to use a standardized test and not let its limits control curriculum and instruction, this can result in a school putting itself at risk for producing lower test scores, with negative political consequences.

Some critics say that some children do not do well on standardized tests, despite mastery of the material, due to testing anxiety or lack of time management or test-taking skills. This reflects the fact that tests cannot directly measure student knowledge, only the ability of students to apply knowledge in a stressful situation.

Some parents are willing to pay thousands of dollars to prepare their children for tests, a financial barrier that may give children of more wealthy parents an advantage compared to less affluent families. However this criticism would probably apply even more to testing alternatives such as portfolios or essays. Many studies also show that test coaching has little effect on scores on well-buih tests. The ability of wealthy families to pay for higher-quality education is not specifically related to standardized testing.

What is the main idea of paragraph 5 ()

A.We should have more testing alternatives other than standardized ones

B. The effectiveness of test coaching varies from student to student

C. The wealthy families have the right for better education

D. The growing influence of test preparation is also a concern for some