A. water
B. carbon dioxide
C. carbon monoxide
D. oxygen
A. live in very hot temperatures
B. live in very cold temperatures
C. manufacture oxygen
D. all of the above
A. the algae have done their work
B. the atmosphere becomes cooler
C. there is oxygen
D. it rains there
A. discuss the advantages and disadvantages of skyscrapers
B. compare skyscrapers with other modern structures
C. describe skyscrapers and their effect on the environment
D. illustrate various architectural