The right answer, but an incoherent reason.b) All x such that x>= 0 : I think closed, because then 0 cannot have neighborhood?
Right idea, say it a little better.c) all x such that either x<0 or x>=1 neither , because one side is open and the other is closed?
Right idea, say it a little better.d)all rational numbers: neither?? because both rational irrational can be neighborhood
If this were open then wouldn't it's complement, the rationals, be closed?e)all irrational number: open