Is a naturally occurring gas that's found in most soils and rocks and can cause lung cancer.
a. radon
b. hydrogen
c. carbon monoxide
d. nitrogen

The answer is Radon. Radon is an odorless, colorless and tasteless gas. It is the heaviest among the noble gases. It is, in fact, radioactive. Radon is considered to be a health hazard. It is so radioactive that further studies become very difficult. When radon decays, radon progeny is produced. These new substances stick to the surfaces of dust particles in air. When inhaled may stick to the lung and airway walls. 

The geographic feature in the westernmost corner of kenya is answer: the great rift vally

Humans have survived and thrived in mexico city by using technology to create greater access to land. when the spanish conquered the aztec capital, tenochtitlan, in the 16th century, they built mexico city by draining the lakes and filling in the lake water to create more arable land for agriculture. this technique of land reclamation has continued to be fundamental to human civilization in mexico city.