Many types of obstacles hinder biomedical scientists from solving health-related challenges. Money that is needed for researches is one of them and you must cooperate with funding agencies. For innovative work you must think outside the box. Also you need to spend too much time for "paperwork".
A hairstreak butterfly my dear.
I say neither because they seem to be the same bird but ill go with B anyway
A) there is a cell and a virus
B) the virus attaches on the receptor on the cell membrane of the cell
C) the virus injects its genetic material in the cell