Which of the following explain why mars does not have a balanced greenhouse effect?
a. mars has an iron-rich core.
b. most of the water is locked in a permafrost layer underground.
c. plate tectonics prevents the release of carbon back into the atmosphere.
d. there are no active volcanoes sending carbon dioxide back into the atmosphere

Which pronoun has an unclear antecedent in the following sentences? the sixth-grade students liked volunteering their time to read to the elderly people in the hospital. it made them happy. a. their b. it c. them d. no unclear antecedents

After fidel castro became the leader of cuba, many cubans moved to the united states. why did cubans leave their home country? a. job opportunities b. religious reasons c. political reasons d. educational opportunities

Of the following choices, which ones are characteristics of west african society? select all that apply. a. arabic was the main language used when trading with other societies. b. christianity was the only religion practiced in villages. c. slaves had no rights and were only given specific farming tasks. d. skilled workers were a higher level in the caste system than traders. e. religious rituals encouraged the honoring of ancestors.