How do you find the meaning of words using context clues?

Part of reading comprehension involves using the other words in a sentence or passage to understand an unknown word. An author often includes hints, or clues, to help the reader expand vocabulary and grasp the meaning of the passage. Skill in using context clues enables a reader to comprehend advance texts. ( I GOT THIS FROM GOOGLE.)

the gas pressure p, gas volume v, and gas temperature t are given in the formula:   pv=nrt,

r is the gas constant, and n is the number of gas moles.

if the container is cooled and remains under atmospheric pressure, where r is a constant that does not change, the volume of the container remains the same, the conclusion is drawn that, with all other values ​​unchanged, the number of gas moles n, is decreases.

the right answer is a.