« on: November 22, 2009, 10:52:37 PM »
The first one:
The conclusion of the passage states that if an amateur astronomer is buying a telescope for planetary observation, then he/she should buy the exodus. Image quality of the Exodus telescope was stated to support this conclusion. If it were true, as answer choice C says, that many serious amateur astronomers have no intention of buying a telescope for astronomical observation, that would not weaken the conclusion of the argument, because the conclusion merely states that amateur astronomers who intend to observe the planets should buy the exodus due to its superior image quality. Those who do not intend to observe the planets are beyond the scope of the argument.
On the other hand, let's now assume that it's true that image quality is only one of several factors that taken together should determine the choice of telescope for amateur astronomers, as choice B says. If that were true, then it weakens the conclusion that an amateur astronomer should purchase the Exodus telescope simply because it has better image quality. In other words, it's not enough to know about image quality when determining which telescope to buy, other factors must be included along with it. So, if choice B were true, the conclusion of the passage is seriously weakened.
The second one:
The argument said the various brands of motor oil were tested to determine which oil is best for a car. All brands did equally well in protecting the engine from wear. Therefore, according to the passage, people should buy the cheaper brand of oil since all brands functioned equally well.
But what if it were true that oil has benefits other than protecting the engine from wear. (choice e) If that were true then it's possible that more expensive oil might be more beneficial for those benefits, even though all brands of oil functioned equally well in protecting the engine from wear. In that case, one might want to purchase the more expensive oil for the additional benefits. So, the conclusion, that one should purchase the cheaper oil is seriously weakened if it's true that motor oil has benefits other than protection from engine wear.
Choice B tells us that there are tests other than the one conducted which could reliably test the quality of motor oil. This does not weaken the argument, however, because it does not state that the test conducted in the study was unreliable, it simply states that other reliable tests might also be available.