ans should be B
rest are different types of distributed computing
The two concepts parallel computing and distributed computing are very closely related; they mostly come from very different backgrounds.
Parallel computing means that different activities happen at the same time. The term was mostly used in scientific computing (consumer computers until very recently simply were not parallel) where it typically means: spread out a single application over many many cores/processors/processes to get it done bigger/faster. Current big parallel computers have 100 thousand to a million parallel processors/cores/threads/whatever.
Distributed computing comes from the business world where you have distributed systems such as airline reservation systems, where many people access and modify the same data at the same time. The machinery involved here is typically much looser coupled, and the activities in a distributed system are typically far less synchronized
