Complete the following statements about innate immunity by selecting the appropriate term from each dropdown list.

Innate immune mechanisms include several types of barriers to pathogen entry. Mechanical barriers include skin and the mucous ""(A) lining"" the respiratory, digestive, and urinary tracts. The excretions of ""(B) sebaceous glands"" and sweat glands in the skin contain chemicals that kill certain bacteria on the skin. The stomach has an ""(C) acidic"" pH, which kills many types of bacteria or inhibits their growth. Resident microbes that normally reside in areas such as the intestine and vagina take up nutrients and prevent ""(D) pathogens"" from taking up residence.

A) endothelium
B) sebaceous glands
C) alkaline
D) pathogens