Assume as what happens in a pot of water as it get heats.. hot becomes less dense, rises and cools, becoming more dense then sinks- that's called CONVECTION
So D- is the right answer
I hope this helps
gymnoseperms meaning "naked seeds" are a diverse group of seed plants and are paraphyletic. paraphyletic groups are those in which not all members are descendants of a single common ancestor. gymnoseperm seeds are not enclosed in an ovary; rather, they exposed in cones or modified leaves
Answer:
A.The hole in the ozone layer
Explanation:
• Montreal protocol is an international treaty that was signed to control the use of substances that are resulting in the depletion of the ozone hole.
This treaty was signed in the year 1987 and became effective form 1989.
• Since the time that this treaty has come into force, there has been a significant improvement in the ozone hole that was observed over Antarctic as it's size has decreased.
• This improvement has been possible because the treaty helped to phase out chemicals such as chlorofluorocarbons, carbon tetrachloride, etc. that are responsible for ozone hole depletion.
Occurs naturally on earth
