People who have been vaccinated still need to be vaccinated again when they encounter the same biological warfare agent (pathogenic microorganisms or toxins used in warfare) because________
A. These people have lost their immunity
B. These people did not form memory cells
C. The original vaccination was unsuccessful
D. These pathogenic microorganisms mutate rapidly and have strong variability
Answer:D
People who have been vaccinated still need to be vaccinated again when they encounter the same biological warfare agent (pathogenic microorganisms or toxins used in warfare) because________
A. These people have lost their immunity B. These people did not form memory cells C. The original vaccination was unsuccessful D. These pathogenic microorganisms mutate rapidly and have strong variability