For a given function an asymptote is a value for which the denominator of the function becomes zero.
And so the function becomes undefined.
Also if the denominator of any fraction is zero, the value of the fraction goes on to become infinity or very large.
A function has vertical asymptotes at x-values for which it is Undefined and near which the function's values become very Large positive or negative numbers.
Option C) is the right answer.
