Antibiotics

Step 1: Identify the substances.
Antibiotics are substances used to kill or inhibit the growth of bacteria.
Streptomycin, chloromycin, and penicillin are antibiotics.
Step 2: Analyze the options.
Aflatoxin is a toxin produced by fungi, not an antibiotic. Streptomycin, chloromycin, and penicillin are all used to treat bacterial infections.
Conclusion: The correct answer is (D) Aflatoxin.