Concept:The Montreal Protocol is an international treaty designed to protect the Earth’s ozone layer by controlling harmful chemicals.Explanation:The main aim of the Montreal Protocol is to protect the ozone layer. It was adopted on September 16, 1987, to regulate the production and use of substances that deplete the ozone layer. Initially signed by 46 countries, it now has nearly 200 signatories. This treaty focuses on phasing out ozone-depleting chemicals like chlorofluorocarbons (CFCs). It does not directly address biodiversity, global warming, or climate change, though it indirectly helps climate by reducing some greenhouse gases.Answer:A. Protection of the Ozone layer