The alpine biome is characterized by short, slow-growing plants and warm-blooded animals. Though it is widespread in Europe and Central Asia, the alpine biome exists
along the equator in only a few small areas in South Arherica. The alpine biome is
rare along the equator because —

b). only regions with extremely high altitudes can have the required climate there because of the high temperatures near the equator.

Explanation:

As per the question, the key reason for the alpine biome being scarce down the equator is the 'higher temperatures in the equatorial and nearby regions.' Alpine biomes are majorly found in the regions having higher altitudes(around 10,000 feet) like mountain regions which provide adequate climatic conditions for their survival while the equatorial regions fail to provide it. Thus, such plants are not found commonly across warm areas because such high temperatures are directly opposite to the conditions required for such biome to survive. Hence, option b is the correct answer.