(a) Let \(D\) be an open connected set in \(\mathbb C\), and \(f\) a holomorphic function on \(D\). Show that if either the real or imaginary part of \(f\) is constant, then \(f\) is constant.
(b) Let \(f\) be an entire function. Show that if either the real or imaginary part of \(f\) is a bounded function then \(f\) is a constant.