Final answer:
The question lacks a specific function to evaluate the limits for a=1, 2, 4, 6. Limits are calculated based on a function's behavior as x approaches a number, and without this, no determination can be made about the given options.
Step-by-step explanation:
To determine the limits of a function as x approaches various values of a, we need a specific function to evaluate. Given the information provided, there is no explicit function mentioned for which we could calculate the limits for a = 1, 2, 4, 6. Typically, limits involve finding the value that a function approaches as x gets infinitely close to some number a. For the function y = 1/x, mentioned in the reference, we know that neither x nor y can equal zero. The function has an asymptote at x = 0, where the limit does not exist because the function's value tends towards infinity. Without a specific function provided for the other cases, we cannot determine whether the limits are as given in options (a) through (d), or whether they exist at all. The question may be misformatted or lacking crucial information needed for a proper evaluation.