The right option is; D. Virus are not killed by antibiotics
Antibiotics are unhelpful for treating the common cold because virus are not killed by antibiotics.
Antibiotics are medications that can destroy or inhibit the growth of bacteria. Antibiotics are only used for infections caused by bacteria. Antibiotics do not kill or work on viruses, such as the virus that cause common cold. This is because antibiotics destroy bacteria by directly aiming at its growth machinery but viruses reproduce differently and have different structures. Hence, viruses are not affected by antibiotics.