B) Terraformation- the greening of the red planet would be the most ambitious engineering project in human history. This feat may be raising the temperature from-60 degrees to -40 degrees. One way to begin this is to build chemical factories, power them with small nuclear reactors that will pump out greenhouse gases to cover the planet and prevent the escape of heat. Then, as the temperature rises, the atmosphere will become thicker but not thick enough. Hence, an ozone substitute will be manufactured to supplement the atmosphere. When the temperature reaches-25 degrees, tundra vegetation will survive. Later, as the planet warms to -15 degrees, tundra, carbon dioxide, nitrogen, and water will seep from the crust. The atmosphere will continue to thicken and water will pool in canyons. Soon. Mars will have a breathable atmosphere when microorganisms will create soil to sustai plants, and plants will convert the atmospheric carbon dioxide into oxygen. When the temperature reaches -5 degrees, the ice will mekt. Bodies of water will be formed and rain will fall regularly. Trees will be planted, changing the dry red planet into a moist green globe. Terraformation, one of our prodigious dreams, may founder. But suppose it could be done, should it be done?

1. Why is the terraformation of Mars being contemplated by Scientists?

2. What is the key to the terraformation of Mars?

3. What are its stages?

4. Why will carbon dioxide, nitrogen, and water seep from the crust when the planet, warms to 15 degrees?

5. What is the topic sentence? 6 What is the subject?​