Why is the process for developing a vaccine usually lengthy? A. Obtaining the necessary supplies for testing is complicated. B. Recruiting scientists to work on a vaccine project can be difficult. C. Ensuring that a vaccine is safe requires multiple rounds of human testing. D. all of the above

C. Ensuring that a vaccine is safe requires multiple rounds of human testing

Explanation:

Vaccination is the process whereby a substance called a VACCINE is administered in order to prevent a particular disease. The vaccine is actually a substance given to help the body's defense system combat a particular infection or disease. A vaccine, which is usually a harmless strain of a pathogen, prepares the antibodies of an organism to fight against the actual pathogenic organism.

As rightly said in the question, developing a vaccine can be a very long process. This is because the vaccine has to go through series of testing on healthy humans before releasing to the public in order to ascertain that there are no risks or dangers attached to the usage. The process of ensuring that a vaccine is safe requires multiple rounds of human testing, which is time-consuming.

≅200-130 milions years ago pangea splited in 2 continents

i think that is new experiments yield untrustworthy data and should be carefully considered, because you don't know what will happen with the experiments.