Which of the following statements are true?
a. If $A$ is a dense subset of a topological space $X$, then $X \setminus A$ is nowhere dense in $X$.
b. If $A$ is a nowhere dense subset of a topological space $X$, then $X \setminus A$ is dense in $X$.
c. The set $\Bbb R$, identified with the x-axis in $\Bbb R^2$, is nowhere dense in $\Bbb R^2$.
I have tried to find out examples but could not succeed. Please Help.