Which "sphere" is not directly studied in one of the main branches of Earth/space science (geology, astronomy, meteorology, or oceanography) ?

a. biosphere

b. exosphere

c. atmosphere

d. hydrosphere

The correct answer is letter A. Biosphere is not directly studied in one of the main branches of Earth/Space science. This is a branch of science that focuses on living organisms that are living in different populations or communities all over Earth. The other three choices directly study these branches of Sciences.