निम्नलिखित में से किसे नवीकरणीय प्राकृतिक संसाधन (renewable resource) के रूप में वर्गीकृत किया गया 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)?