निम्नलिखित प्राकृतिक संसाधनों में से किसे एक अक्षय (अक्षयशील) संसाधन माना जाता 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)?