Consider two positive-term series ∑an and ∑bn. Which of the following sets of conditions is sufficient to guarantee that ∑n=1∞an converges?
a) 0≤bn≤an for all n and ∑bn converges.
b) 0≤an≤bn for all n and ∑bn converges.
c) an≤bn for all n and ∑bn converges (no restriction on signs).
d) 0≤an≤bn for all n and ∑bn diverges.