3. The extreme of his stock portfolio translated into a display of emotion: on lucrative days he felt ecstatic; on losing days he acted despondent. aggressiveness...consistent
nature...passionate
position...crazy
volatility...mercurial
variation...pacific

volatility...mercurial

Explanation:

The second part of the sentence helps us infer its meaning; it denotes changes in one's mood. From the first part of the sentence, then, we can see that these mood swings mimicked changes in his stock portfolio.

Basically, depending on the balance on his stock portfolio, the person was either ecstatic either depressed.

Now that we've infered the context of the sentence, it's not hard to see that the word pair we're looking for has to do something with changes, variability, inconsistency, tendency to easily fluctuate in short period of the time.

The only pair that could fit in this description is "volatility...mercurial".

ill check : )

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