@ Thanks nye8870! But I still think D is unnecessary. If there is ONE (or more) student who are "least enthusiastic" and "not most committed", then the course fails to serve its purpose. Thus, it is not necessary to say that "All the least enthusiastic are not most committed". That's D. Could you correct me if I am wrong? @ Could you take a look at our discussion?

Yes I really agree with you! I think it is sufficient but not necessary ! Could anyone explain it?