In the following passage, some of the words have been left out. Read the passage carefully and select the correct answer for the given blank out of the four alternatives.
A brain and nervous system that are poorly developed or insufficiently nourished means low grade of________in our mental processes, just as a poorly constructed or wrongly adjusted motor means loss of power in applying the electric current to its work. We will,_______, look upon the mind and the brain as counterparts of_______other, each performing activities which correspond to activities in the other,_____inextricably bound together at least so far as this life is concerned, and each getting its_________by its union with the other. This view will lend interest to a brief study of the brain and nervous system.
as counterparts of ______other, each performing

Options

A. once
B. only
C. every
D. each

Answer

D