The correct answer is B.
The first two sentences are establishing characteristic shared by both petroleum and coal. The word "however" is used to contrast the similarities already presented with the differences that will be stated in the following sentences.
Well the mood is definitely not peaceful because it says they are in pain. It is not exciting because something bad is happening. It is not cheerful because they are in pain so it has to be oppressive means to be overwhelmed.<span>
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