B

Step 1: Understand what modulus of rigidity is. The modulus of rigidity, also known as shear modulus, is a measure of a material's ability to withstand shear deformation.
Step 2: Compare the modulus of rigidity of various materials. Diamond is known to be one of the hardest materials with a very high modulus of rigidity. It typically has a modulus of rigidity around 478 GPa.
Step 3: Consider other common materials: Metals like steel have a modulus of rigidity around 80-200 GPa, and materials such as wood and rubber have significantly lower values.
Conclusion: Since the modulus of rigidity of diamond is greater than that of all known materials, the correct answer is Option B.