For each of the following queries indicate whether a use of an index would be helpful or not. If so, specify which tables and columns an index should be created on and the best choice between a clustered or unclustered index. You can assume that the system provides that choice:

A. SELECT * FROM Users;

B. SELECT * FROM Posters WHERE userid = 3;

C. SELECT name FROM Publisher WHERE name = 'New York Times';

D. SELECT userid,COUNT(*) FROM Has_read GROUP BY userid;