Answer:
The scenario that would explain that how the people got sick in this case is option "D" that is 'contact with an infected person'.
Step-by-step explanation:
This is just because the virus can enter to our body very easily by contacting with an infected person.It may cause from the breath in air,shaking hand etc.
Option A which is contact with environmental sources may not be a reason of not getting sick because the environment cannot become infected and somewhere the environment can be pure and clean.
Option B which is Contact with an infected animal is also not the reason of getting sick because infected animals cannot spread their disease in humans because their infection and diseases are very different from humans.
Option C which is Contact with a contaminated object can also be a reason somewhere because these objects can spread various diseases.