The body's most important nonspecific defense against pathogens is/are
a. tears
b. mucus
c. saliva
d. skin

Skin is the most important

Hii!! I believe the answer is D. skin. (:

The Calvin cycle cannot operate during the night, as light is needed to convert carbohydrate molecules into chemical energy. However, some plants that have evolved (due to arid conditions) to utilize CAM photosynthesis (Crassulacean acid metabolism)--which the plant shuts it's stomata during the day, in order to reduce evapotranspiration, but open at night, to collect carbon dioxide. Thereby, making the majority of plants unable to compensate like these select few plants--that have evolved to do so.