Which is the most appropriate choice of antimicrobial therapy, when bacterial infection is considered to be a contributor, for use during a moderate-to-severe COPD exacerbation in a 72-year-old man with stage III (severe) COPD and type 2 diabetes mellitus?

a) Moxifloxacin
b) Amoxicillin
c) Trimethoprim-sulfamethoxazole
d) Fosfomycin