複選題33. Which of the following description(s) is/are CORRECT? (A) A vaccine is a biological preparation that provides active acquired immunity to a particular infectious disease. (B) There are four types of COVID-19 vaccines in clinical trials: whole virus particles, protein subunits, viral vector and nucleic acids. (C) COVID-19 is an infectious disease caused by the SARS-CoV-2 virus. (D) Bacteria, viruses, fungi, parasitic worms, insects and snakes are all belonged to pathogens. (E) Allergy is a kind of immune disease.