निम्नलिखित में से कौन सा ऊर्जा स्रोत अपने संचालन चरण के दौरान वस्तुतः कोई वायुमंडलीय प्रदूषण उत्पन्न नहीं करता है?

Prolonged exposure to extreme cold temperatures may result in tissue damage known as frostbite, which is categorized as a:

In the context of ecosystem energy dynamics, which of the following expressions correctly defines Net Primary Productivity (NPP)?