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
A. The exterior surrounding air is heated
B. The building materials are very expensive
C. Construction time is increased
D. Extra air-conditioning equipment is needed