工程师未能及时按照合同约定发出图纸导致承包人违约，这种索赔原因可归结为（）。
A.工程师指令
B.合同缺陷
C.当事人违约
D.合同变更
参考答案：C
氧气、乙炔气瓶能否混放？为什么？
Editorialist: Additional restrictions should be placed on driver’s licenses of teenagers because teenagers lack basic driving skills. Even though drivers of age nineteen and younger make up only 7 percent of registered drivers, they are responsible for over 14 percent of traffic fatalities. Each of the following, if true, weakens the argument that teenagers lack basic driving skills EXCEPT:
A．Teenagers tend to drive older and less stable cars than other drivers.
B．Teenagers and their passengers are less likely to use seat belts and shoulder straps than others.
C．Teenagers drive, on average, over twice as far each year as other drivers.
D．Teenagers cause car accidents that are more serious than those caused by others.
E．(E) Teenagers are likely to drive with more passengers than the average driver.
