<p>Caustic didn’t seem like a good choice because it often connotes acidity and strong bitterness, and vehement better corresponds with emphatic - but considering that that paragraph independently and that caustic can mean “severely critical or sarcastic,” it can’t be said that caustic “does not fit at all.”</p>
<p>I don’t think the Chinese miners were on the SAT, but most of the other stuff in there was. There are definitely a handful of ironic statements in that passage, accompanied with facts that criticize coal.</p>