which of these molecular structures could be found in a lipid, but not in a carbohydrate, protein, or nucleic acid?

"what factors influence the absorption of sunlight at earth's surface? "

How are brightness and size related when it comes to stars

Zachary has been trying to work on an essay for almost three hours, be he can't seem to focus for more than 15 or 20 minutes at a time. what should he do so that the quality of his work doesnt suffer because of poor concentration and lack of energy