Which forest biome is widely designated as the "Lungs of the World" due to its massive carbon sequestration and oxygen production?

Match List I with List II and select the correct answer using the codes given below: List I P. Hekistotherms Q. Mesotherms R. Megatherms S. Microtherms List II1. Cannot tolerate high temperature2. Require high degree of heat throughout the year3. Require moderate temperature for growth4. Require very low temperature and can stand very long winters

Assertion (A): Steppe regions are characterized by dense forest canopy and high arboreal biodiversity. Reason (R): Steppe climates feature low annual rainfall and high temperature variability, favoring grasses over tree growth.