A set A is called clopen if and only if it is both open and closed. a)

Question:

A set A is called clopen if and only if it is both open and closed.
a) Prove that every Euclidean space has at least two clopen sets.
b) Prove that a proper subset E of Rn is connected if and only if it contains exactly two relatively clopen sets.
c) Prove that every nonempty proper subset of Rn has a nonempty boundary.