The correct answer is: C. 150 MPa
Crushing strength is a measure of the ability of a material to withstand compressive forces. It is typically measured in megapascals (MPa). The crushing strength of a good building stone should be more than 150 MPa. This is because building stones are subjected to a lot of compressive forces, such as those from the weight of the building above them. If the crushing strength of the stone is too low, it may crack or crumble under these forces.
Option A: 50 MPa is too low. A stone with a crushing strength of 50 MPa would not be able to withstand the compressive forces from a building.
Option B: 100 MPa is a good crushing strength for a building stone. However, it is not the minimum required strength.
Option C: 150 MPa is the minimum required crushing strength for a good building stone.
Option D: 200 MPa is a very high crushing strength. It is not necessary for a building stone to have this high of a crushing strength.