List the three reasons why a function might be discontinuous at the point x=c

From the question;
we are to state the three reasons why a function might be discontinuous at the point x=c
A funtion f(x) is discontinuous at a point x = c if
1.
[tex]f(c)\text{ is not defined}[/tex]2.
[tex]\lim _{x\to c}\text{ f(c) does not exi}st[/tex]3.
[tex]\lim _{x\to c}\text{ f(x) }\ne f(c)[/tex]If all this condition are statisfied, then the function is discontinuous at x = c