What is the Amazon rain forest often referred to as?

The correct answer is Option (3) → The Lungs of the Planet

The Amazon rain forest in South America is the largest tropical rain forest on Earth. It is so huge that it is called the ‘lungs of the planet’, because its vast plant cover takes in carbon dioxide and gives out oxygen. It holds probably millions of species. Today it is being cut and cleared to grow soya beans and to make grasslands for beef cattle, which is a major example of habitat loss.

NCERT Extract:
Loss of Biodiversity – “… By the time you finish reading this chapter, 1000 more hectares of rain forest would have been lost. The Amazon rain forest (it is so huge that it is called the ‘lungs of the planet’) harbouring probably millions of species is being cut and cleared for cultivating soya beans or for conversion to grasslands for raising beef cattle.”