The correct answer is: A. the remaining sites can continue operating.
A distributed system is a system that is made up of multiple computers that are connected to each other. The computers in a distributed system can be located anywhere in the world. The advantage of a distributed system is that it is more reliable than a centralized system. If one computer in a distributed system fails, the other computers can continue to operate.
Option B is incorrect because it is not always true that all the sites will stop working if one site fails. In a distributed system, the remaining sites can continue to operate even if one site fails.
Option C is incorrect because it is not always true that directly connected sites will stop working if one site fails. In a distributed system, the remaining sites can continue to operate even if one site fails.
Option D is incorrect because it is not a valid option.