Which of the following parts of the eye refract light to focus it in the retina

Write a paragraph about why the respiratory system is important and we need to breathe easily. (guys i really need ) x(

Mucous membranes.. a. cover or line external surface of body. b. line internal body surfaces that are in contact with the environment. c. produce antibodies to combat infection. d. secrete sweat, which has antibacterial enzymes.

Which of these is likely to be the best source of valid health information?