We are asked how passage B relates to passage A. Passage A discusses environmental modeling, the problem of needed computing power, and proposes a possible solution, which is parallel computing.
Passage B is a more general discussion of parallel systems in nature, and how the concept of parallelism is now being applied to computing.
To understand answer D, we should look back to see what the first passage says about the brute force method. It looks like the brute force method refers to the idea that we would need to do millions and millions of calculations in order to successfully look at all the possibilities. This does not relate to the idea of parallel computing- just the idea that we must do many calculations. Furthermore, the need for brute force is only in reference to the problem of climate modeling, not to parallel computing in general.
C, on the other hand, is more general. B offers a broad explanation of the solution proposed in A, and gives us more detail about why parallel systems work. So, C is a good match for our understanding of the passage.
