▶ Your Answer : In the lecture, the speaker contends that the theories suggested in the reading are groundless. This casts doubt on the reading passage's assertion that there are the plausible theories to explain why Scotland built forts using stones that are vitrified.
To begin with, the lecturer asserts that it is unlikley that signal fires were the reason for vitrification. He points out that Scotland people used fires at a few locaion of forts, from only one to two, for communication, so it can't explain why the entire forts were vitrified. This is in contradictory to the reading's point that signal fires were the cause of vitrification.
In addition, the speaker points that it is untrue that vitrification was caused by lightning. To be specific, it was impossible for lightning to make the very extensive forts become vitrified. Also, resorting to lightning as main evidence of the uneven appearance of the wall in forts is wrong, because Scotland forts are old and thus it is reasonable that these forts are equipped with the uneven appearance of the wall. This is direct opposition to the reading passage's argument that lightning was a key factor in vitrification.
Lastly, the lecturer maintains that it is hard to say that using volcanic rock caused the forts to become melt and fused, so it could bring about vitrification. He supports his idea by saying that there is no evidence that volcanic activities occured at the near Scotland forts, which means that Scotland people had to move large and heavy volcanic locks from distant areas to the construction site of forts. However, it was impossible to move the huge amount of rocks from too distant areas. This rebuffs the reading passage's insistence that using volcanic rock triggered the forts to become melt and fused, so it could lead to vitrification.
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