In the ideal double-slit experiment, when a glass plate (refractive index 1.5) of thickness \[t\] is introduced in the path of one of the interfering beams (wavelength\[\lambda \]), the intensity at the position where the central maximum occurred previously remains unchanged. The minimum thickness of the glass plate is

• A. \[2\lambda \]     
• B. \[2\lambda /3\]
• C. \[\lambda /3\]    
• D. \[\lambda \]