The fluid that lines the alveoli contains a substance that reduces surface tension known as

I'd say that it is the "surfactant"

The sides of the double helix of the DNA are made up of sugar and phosphate backbone. The sugar is deoxyribose in case of DNA and ribose in case of RNA. The bridges are formed of the nitrogenous bases; adenine, guanine, thymine, and cytosine. RNA contains uracil n place of thymine.