Which one of the folowing participate in the body's second line of defense?

Question

A.Tissue liningsof the respiratory system
B. Interferons
C. Skin cells
D. Saliva

http://www.amnh.org/nationalcenter/infection/03_inf/03_inf.html

For virus, B is the choice, as interferons are part of the immune system.

http://www.amnh.org/nationalcenter/infection/03_inf/03_inf.html

For virus, B is the choice, as interferons are part of the immune system.

A, B, and D are all the first line of defense

i meant a,c, and d