Step 1: Understanding ventricular system.
The brain contains a series of interconnected cavities called ventricles that circulate cerebrospinal fluid. Step 2: Connection between ventricles.
Each lateral ventricle communicates with the third ventricle through an opening known as the interventricular foramen or foramen of Monro. Step 3: Conclusion.
Hence, the correct answer is (B) foramen of Monro.