Bunuel wrote:

Five persons sat next to each other around a circular table to play cards. Did Grace sit next to Bill?

(1) Dora sat next to Ethyl and Carl.

(2) Grace sat next to Carl.

The answer should be A.

If you know three of the five people are sitting adjacent to one another, the other two people must have to be sitting on the other side next to one another. The other two people must be Grace and Bill, given that neither one are part of that group of three people we know are sitting next to one another.

The second statement is not sufficient. Grace sitting next to Carl tells us nothing about where Bill is sitting.