Question

calcium 2
phosphorus 1
all other elements 4
which two elements, combined, make up 75% of the human body?
carbon & calcium
oxygen & hydrogen
oxygen & potassium
calcium & hydrogen

Explanation:

Oxygen and hydrogen are the two most abundant elements in the human body, mainly due to the presence of water ($H_2O$) which makes up a large - part of body mass.

Answer:

B. oxygen & hydrogen