问题 单项选择题

司可巴比妥钠的测定方法如下:取本品0.1mg,精密称定,置250ml碘瓶中,加水l0ml,震摇使溶解,精密加溴滴定液(0.1mol/L),再加盐酸5ml,立即密塞并震摇1min,在暗处静置15min后,加碘化钾试液l0ml,立即密塞,震摇均匀后,用硫代硫酸钠滴定液(0.1mol/L)滴定,至终点时,加淀粉指示剂,继续滴定至蓝色消失,并将滴定结果用空白校正,即得。则:每1ml溴滴定液(0.1mol/L)相当于mg的司可巴比妥钠(相对分子量为260.27)

A.260.3

B.26.03

C.130.1

D.13.01

E.1.301

答案

参考答案:D

问答题 简答题
阅读理解

阅读理解。

     At age 61, identical twins Jeanne and Susan no longer look exactly alike. Susan smoked for many years

and is an admitted sun worshipper, whose habits Jeanne does not share. A new study of twins suggests you

can blame those coarse (粗糙的) wrinkles, brown or pink spots on too much time in the sun, smoking, and

being overweight.

     Because twins share genes, but may have different exposures to environmental factors, studying twins

allows an "opportunity to control for genetic susceptibility (易受影响性)," Dr. Elma D. Baron, at Case

Western Reserve School of Medicine in Cleveland, Ohio, and his colleagues explain in the Jatest issue of

Archives of Dermatology.

     Their analysis of environmental skin-damaging factors in 65 pairs of twins hints that skin aging is related

more to environment and lifestyle than genetic factors.

     But when it comes to skin cancer, the researchers say their findings support previous reports that both

environment and genes affect skin cancer risk.

     Baron's team examined facial skin of 130 twins, 18 to 77 years old, who lived mostly in the northern

Midwest and Eastern regions of the US, who were attending the Twins Days Festivalin Ohio in August 2002.

At this time, each of the twins also separately reported how their skin burned or tanned (晒黑) without

sunscreen, their weight, and their history of skin cancer, smoking, and alcohol drinking. The study group

consisted of 52 fraternal (异卵双生) and 10 identical twin pairs, plus 3 pairs who were unsure of their twin

status.

     From these data, the researchers noted strong ties, outside of twin status, between smoking, older age,

and being overweight, and having facial skin with evidence of environmental damage. By contrast, sunscreen

use and drinking alcohol appeared related to less skin damage.

     Baron and his colleagues say the current findings, which highlight ties between facial aging and potentially

avoidable environmental factors-such as smoking, being overweight, and unprotected overexposure to the

sun's damaging rays-may help motivate people to minimize these risky behaviors.

1. Which of the following is true according to the passage?[ ]

A. Jeanne and Susan share all the habits including smoking.

B. Skin aging is related more to environment and lifestyle than genetic factors.

C. Only identical twins can take part in the research.

D. Sunscreen use cannot help people have less skin damage.

2. Why did Baron's team do the research on twins? [ ]

A. Twins are more likely to suffer from skin cancer.

B. It may guarantee the research is not influenced by genetic factors.

C. It gives others an opportunity to control twins' genes.

D. It helps find twins are exposed to different environments.

3. What can you infer from the last paragraph? [ ]

A. This research makes people aware of dangerous lifestyles.

B. The environmental factors are unavoidable.

C. Being exposed to the sun is absolutely damaging.

D. There is little relationship between skin aging and environment.

4. The passage is mainly concerned with _____.[ ]

A. skin cancer and environment 

B. identical twins research

C. aging skin and environmental factors

D. genes and lifestyles