It's a subtle point in the language: option A says that this constraint prevents any PUT or DELETE operations from occuring [end of statement]. However, this isn't true, because any user authenticated under the 'admin' role can use PUT and DELETE operations and they will be successful (this is the correct option D). So A is incorrect because it doesn't stop any PUT or DELETE, only those where the user is not in the 'admin' role. Option D is the correct alternative.
I admit the question could have been slightly better phrased, but the answer made it clear to me what was/wasn't true when I re-read it.
Charles Lyons (SCJP 1.4, April 2003; SCJP 5, Dec 2006; SCWCD 1.4b, April 2004)
Author of OCEJWCD Study Companion for Oracle Exam 1Z0-899 (ISBN 0955160340 / AmazonAmazon UK )