What is terraforming and how can we do it on Mars?

Explanation:

To successfully terraform Mars, the atmosphere would need to be raised enough so that humans could walk around without spacesuits. But although tripling the Red Planet's atmospheric pressure might sound like a lot, it's only one-fiftieth of the CO2 necessary to make the atmosphere habitable to Earth creatures.

answer; i believe the correct answer is (a) the correlation between the cause variable and outcome variable is zero;

answer; severe;