पर्यावरण विज्ञान में, 'स्मॉग' (SMOG) शब्द मुख्य रूप से किन दो घटकों के संयोजन से बना 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)?