Let {aₙ} be a sequence. Which statements are equivalent to "is bounded above"?
a) There exists M ∈ R such that aₙ≤M for all n.
b) The sequence {aₙ} has a finite limit.
c) The sequence {aₙ}is monotonic and convergent.
d) There exists N ∈ N such that ∣aₙ∣ ≤ N for all n.