Answer: option A - the individuals who survived were able to produce antibodies against the Ebola
Step-by-step explanation:
Carefully observe the sentence structure
from which the inference was made "the individuals who survived were able to produce antibodies against the Ebola"
Note that the SURVEY focused only on INFECTED INDIVIDUALS.
So, assume 100 people were present during the outbreak. These 100 were also infected, but ONLY about 80 died - inferring that the REMAINDER (20 individuals) of those infected "escaped" death.
This "escape" or survival is definitely because the individuals were able to produce antibodies against the Ebola