When we returned home from our six month vacation abroad, we found several drinking glasses shattered in place on the kitchen shelf. This can only happen during a sonic boom or when there is an earthquake. This must have been the loud noise that we heard not long after we drove off to the airport on the night we left for our vacation. Since there was no report on the car radio that night about earthquakes in the area, which always get a lot of attention, the glasses must have been shattered by a sonic boom, which is so common that it's never reported.
The speaker's conclusion about the "loud noise" assumes which of the following?
A. It is easy to tell the difference between glass shattered by an earthquake and glass shattered by a sonic boom.
(A) is incorrect. The author's conclusion is that the "loud noise" they heard must have been a sonic boom, based on three pieces of evidence: (1) the glasses were found shattered, which can only happen as a result of either an earthquake or a sonic boom; (2) they heard the "loud noise" on the night they left, and (3) there was no report of an earthquake on the news that night. What is missing is any definitive proof that this particular "loud noise" in fact caused the glasses to break, not whether it is easy to tell whether they broke as a result of one cause or the other. The author assumes the noise was a sonic boom because he also assumes that it broke the glasses, that it couldn't have been an earthquake because no earthquake was reported, and there is nothing besides a sonic boom or earthquake that could have broken the glasses.
B. A sonic boom always causes more damage in the house than an earthquake does.
(B) is incorrect. The stimulus provides no evidence of "more damage in the house" besides the broken glasses. Only the three items of evidence mentioned above are presented as evidence. Even if earthquakes cause more damage than sonic booms, the latter could still have shattered the glasses in this case. Further, the argument claims the cause of the "loud noise," not cause of the shattered glasses.
C. The drinking glasses on the shelf were shattered because they were not safely protected.
(C) is incorrect. The issue is not what could have prevented the glasses from shattering; the issue is whether the "loud noise" was an earthquake or a sonic boom (or perhaps something else entirely). Whether the glasses could have been protected is irrelevant to the question of which natural phenomenon occurred that caused them to break.
D. No earthquake has occurred since the night the family left on their vacation.
(D) is correct. The argument is that the "loud noise" had to have been a sonic boom and cannot have been anything else. The fact that the glasses were found broken (which could have had one of only two causes), the fact that they heard the "loud noise" on the night they left, and the fact that no earthquakes were reported that night, led the author to conclude that the noise must have been a sonic boom. However, the author is ignoring what should be an obvious alternative possibility: that some other event that occurred while they were away, not the "loud noise" they heard the night they left, broke the glasses. If the glasses could have been shattered by another event subsequent to the "loud noise," then the fact that they were shattered alone cannot be taken as evidence that the "loud noise" had to have been either a sonic boom or an earthquake. The "loud noise" could have been anything if it was not the event that shattered the glasses. The fact that no earthquake was reported on the night of the "loud noise" tells us that it was probably not an earthquake, but unless it can be shown that the same "loud noise" shattered the glasses, the author cannot conclude that it must have been a sonic boom.
E. Every time there is an earthquake in the area, some of the kitchen glassware will be shattered.
(E) is incorrect even if it is probably true. The author is not basing his conclusion, that the noise was a sonic boom, on this fact. Even if it's possible for all of the kitchen glassware to survive an earthquake, this would not undermine the author's conclusion that the "loud noise" was a sonic boom.
