Answer:
C. They are easily treated with antibiotics. (Although it depends on whether antitoxin counts as an antibiotic)
Step-by-step explanation:
A. There is no vaccine for botulism.
B. Smallpox has been eradicated by vaccination so it can't be used for bioterrorism.
C. Botulism is not treated by an antibiotic but rather an antitoxin which stops further damage rather than fixing previous damage.
D. Anthrax and smallpox are treated with antibiotics so they aren't resistant.