The dawn of the oil age was fairly recent. Although the stuff was used to waterproof boats in the Middle East 6,000 years ago, extracting it in earnest began only in 1859 after an oil strike in Pennsylvania. The first barrels of crude fetched $18 (around $450 at today’s prices). It was used to make kerosene, the main fuel for artificial lighting after overfishing led to a shortage of _____ blubber.
문제 2 :
The tour promised spiritual experiences with humpback ______ and other cetaceans, but all we saw were seagulls and a dead sea otter.