Both petroleum and coal are made up of complex carbon-based molecules, and both originated with living creatures of some kind. B
oth are vital sources of energy for the modern world and both were formed by geologic processes over millions of years. However, petroleum was mainly formed from the remains of ocean-dwelling microorganisms. Coal, on the other hand, originated from decayed vegetation in ancient swamps and bogs. In any case, it took millions of years for both coal and oil to be produced. This is the case because it took that much time for overlying sediments to produce the unimaginable heat and pressure that would one day allow us to harvest these energy resources. What is one clue word or phrase in the passage that indicates a contrast?
<span>University presses have rigorous peer review processes. The members in these presses evaluate each other's work to make sure everyone is competent in their field. If they are not competent enough they will be replaced by more skilled applicants. This strategy keeps the level of quality high.</span>
