[单项选择]

Some oil companies plan to get rid of some of the pollution they produce by pumping it into rocks deep inside the Earth, where they say it will stay for thousands of years. Other people, though, aren’t so sure this is advisable; environmental groups say that putting this pollution back into the Earth is a bad idea.
When oil burns, it doesn’t just produce heat: it also produces carbon dioxide. Carbon dioxide is a natural part of the air, but because people burn so much oil, there’s too much carbon dioxide in the air. This extra carbon dioxide is pollution; some scientific studies show that carbon dioxide is one of the "greenhouse gases ’that is causing the Earth’s temperature to rise.
Environmentalists say that the oil companies’ plans may not work. The oil companies say they are making sure that the gas will never escape, but environmentalists wonder how the oil companies can be so sure that the gas won’ t seep into t
A. objective
B. indifferent
C. confused
D. critical