Organic macromolecules called are insoluble in water, are often found in biological membranes and other waterproof coverings, and have the ability to store energy for extended periods of time.

The key words here are insoluble in water and waterproof. Substances that aren't soluble in water are typically not polar, like hydrocarbons. Lipids are made entirely from long chains of carbon and hydrogen, sometimes with a polar phosphorous at one head. That is why the answer must be lipids.

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