The signum function is given by\(sgn\left( x \right) = \left\{ {\begin{array}{*{20}{c}} {\frac{x}{{\left| x \right|}};x \ne 0}\\ {0;x = 0} \end{array}} \right.\)The Fourier series expansion of \(sgn\left( {cos\left( t \right)} \right)\) has

• A. only sine terms with all harmonics
• B. only cosine terms with all harmonies
• C. only sine terms with even numbered harmonies.
• D. only cosine terms with odd numbered harmonies