If you read the sentence very clearly, it says that
“Everyone knows that if there was another world war, it would be fought over water. It plays such a big role in our lives. Yet, ironically, we do not know much about water.”
From this we can understand that the the blank describes the position of water in human life. Since it is widely agreed that if there is another world war, it would be waged over this precious resource.
This is an important explanation context clue that describes how important water is in our lives. It is important to such a magnitude that the next world war might be fought over this important resource.
Water is so precious that it can become the root of all conflicts.
To choose the right options, it is important to know the meaning of the words.
Nemesis - The cause for someone’s or something’s downfall.
Water has been described as the most probable reason for the next world war. Therefore, this word definitely fits the blank.
GREedge Pro Tip: Now that you have one word zeroed in, look only for synonyms of this word.
Relief- Respite or break
Since water could be the cause of the next world war, the word ‘relief’ will not fit. In fact, it’s quite the opposite and can therefore be eliminated!
Affliction - Something that causes pain, damage or harm
Synonym Alert! This word could surely fit as water is a precious resource that can be the root cause for the next world war, causing great devastation.
Antagonist - Opponent or Rival
Water would become so scarce that people would fight over it. Thus, it might be the indirect cause of destruction, not a direct antagonist.
GREedge Pro Tip: Since you know this word is not a perfect fit, look for synonyms of this word and eliminate them!
Manipulator - Someone who controls or influences others
This word is unrelated to the context mentioned, mainly because scarcity of water would the root cause for the next world war. Water as such is not directly influencing or manipulating the course of events.
Competitor - Contestant or Rival
Again, this word is a synonym to the word ‘Antagonist’. Water is not a competitor, but it is the object of competition. So, it doesn’t fit.
