How were scientists able to identify how the virus is transmitted? What conclusions have the Chinese Center for Disease Control and Prevention been able to reach through its observation and study?

Answer to first part of question:

Scientists were able to identify how the virus is transmitted by possibly referring back to previous similar viruses/illnesses and could have tested it among the people.

Ithink option a is correct because you cannot donate a different blood group than yours because it won't match.option a says betsy can donate to mark. they have the same blood group so donation can happen.