For which of the following functions f can we define f(a) so as to make f continuous at a? For those we can, find the value of f(a) that makes f continuous at a. For those we can't, enter none.

A) f(x) = 1 / x
B) f(x) = √{x}
C) f(x) = |x|
D) f(x) = (x² - 4) / (x - 2)