The correct answer is A. Carbon dioxide is called a greenhouse gas because it is transparent to sunlight but traps heat. This means that sunlight can pass through the atmosphere and reach the Earth’s surface, but the heat that is reflected back from the Earth’s surface is trapped by the greenhouse gases in the atmosphere. This trapped heat causes the Earth’s temperature to rise.
Option B is incorrect because carbon dioxide is not transparent to heat. It absorbs heat and traps it in the atmosphere.
Option C is incorrect because carbon dioxide is not used in greenhouses to increase plant growth. In fact, carbon dioxide is a major contributor to global warming, which is causing the Earth’s temperature to rise and is having a negative impact on plant growth.
Option D is incorrect because carbon dioxide is not transparent to both sunlight and heat. It is transparent to sunlight but absorbs heat.