请教两道陈向东逻辑书里的题 It has been hypothesized that much of the matter in the universe is "dark",i.e.,unseen. Studies have shown that galaxies in many galaxy clusters are moving faster with respect to one another than they would if visible stars constituted all their mass. The studies suggest that the galaxies are moving under the gravitational influence of unseen mass in consilerable quantity. Which of the following is an assumption underlying the passage above? (A)Measurements of the speed of moving galaxies are extremely unreliable. (B)The workings of gravitational forces are not particularly well understood. (C)The aggregate mass of visible stars in the galaxies mentioned above can be estimated with some confidence. (D)The general compoosition of unseen matter in the universe has been determined. (E)Without exception,the galaxies mentioned above move toward one another.

陈向东逻辑书里的题，答案是C，可是我看了中文还是推不到。郁闷ING。

A recent report determined that although only three percent of drivers on Maryland highways equipped their vehicles with radar detectors,thirty-three percent of all vehicles ticketed for exceeding the speed limit were equipped with them.Clearly,drivers who equip their vehicles with radar deterctors are more likely to exceed the speed limit regularly than are drivers who do not. (A)Drivers who equip their vehicles with radar detectors are less likely to be ticketed for exceeding the speed limit than are drivers who do not . (B)Drivers who are ticketed for exceeding the speed limit are more likely to exceed the speed limit regularly than are drivers who are not ticketed. (C)The number of vehicles that were ticketed for exceeding the speed limit was greater than the number of vehicles that were equipped with radar detectors. (D)Many of the vehicles that were ticketed for exceeding the speed limit were ticketed more than once in the time period covered by the report. (E)Drivers on Maryland highways exceeded the speed limit more often than did drivers on other state highways not covered in the report. 答案是B。请教推法，看了解析觉得不是很清晰。

1 To compare the moving rates of two types of galaxy, unseen and visible, we must know the respective quantity of mass for each one, since, as it stated in the last sentence, mass constitutes influencial factor to the movement of galaxy. Now, since we get the mass quatity of unseen galaxy and also know unseen galaxies are moving faster than visible ones, then we must be informed of the mass quatity of visible galaxy as a statistically comparable basis.

2 Sort of like a math problem. ticketed drivers = x all drivers = y

then, likelihood of being ticketed for drivers with radar = 33%x / 3%y

likelihood of being ticketed for drivers with no radar = 67%x / 97%y

obviously, the former is larger than the latter. Plus the key B ( the likelihood of being ticketed is the same to that of exceeding speed limit REGULARLY), then the conclusion can be established reasonably.