Thanks for the question! Let’s take a look at what passages A and B are doing. Passage A is telling us about complex calculations, and the last paragraph tells us about complex calculations being done on computers connected to each other via the Internet. Each computer does some work individually on their share of the overall problem.
Passage B is telling us about solving problems with parallel processing in various contexts, ending with a discussion of parallel computing, which is when a bunch of computers work together to solve on a computationally complex problem. Sound familiar? That's because it is. A solution to a complex problem is proposed in passage A—using computers in parallel. The ideas in passage B, parallel processing, are what underlie that idea. This is what (C) tells us—passage B helps provide a rationale for the solution in passage A.
Hope this helps! Feel free to ask any other questions that you might have.
