Answer:
B. Están
Step-by-step explanation:
Remember that in spanish we have estar, as translation for the verb "be" and in depends on how is it being used that you should chose ser or estar, in this case when you talk about sickness, you don´t say que "Es" enfermo, rather than "Está" because sickness is transitory, so you have to conjugate the verb estar for the third person in plural:
Yo estoy
Tu estás
El/ella Está
Ellos Están
So the correct option is "B.Están"