We can use process of elimination:
a does not work as when x \to \infty the inequality will always hold for large values of x
b does not work as when y \to \infty the inequality will always hold for large values of y
c does not work because of the same argument as (b)
And since a, b, and c all don’t work, d must be the answer.
Referred by @AwesomeLife_Math
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Lovely work!
I could not solve this problem because I had read the inequality as an equality. 
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Fantastic 
welcome to CleanSlate!!
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