In the Young's double slit experiment, if the phase difference between the two waves interfering at a point is\[\phi \], the intensity at that point can be expressed by the expression

• A. \[I=\sqrt{{{A}^{2}}+{{B}^{2}}{{\cos }^{2}}\varphi }\]       
• B. \[I=\frac{A}{B}\cos \varphi \]
• C. \[I=A+B\cos \frac{\varphi }{2}\]
• D. \[I=A+B\cos \]