The following equations represent progressive transverse waves \[{{Z}_{1}}=A\cos (\omega \,t-kx)\], \[{{Z}_{2}}=A\cos (\omega \,t+kx)\], \[{{Z}_{3}}=A\cos (\omega \,t+ky)\] and \[{{Z}_{4}}=A\cos (2\omega \,t-2ky)\]. A stationary wave will be formed by superposing [MP PET 1993]

• A. \[{{Z}_{1}}\] and \[{{Z}_{2}}\]
• B. \[{{Z}_{1}}\] and \[{{Z}_{4}}\]
• C. \[{{Z}_{2}}\] and \[{{Z}_{3}}\]
• D. \[{{Z}_{3}}\] and \[{{Z}_{4}}\]