वायु प्रदूषण के खिलाफ आमतौर पर इस्तेमाल किए जाने वाले सुरक्षात्मक मास्क में किसका उपयोग किया 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)?