Introduction: write one sentence to introduce what the graph shows. Just paraphrase the question statement (i.e. change a few words).
Body: compare all 3 countries in 1940, then in 1990.
Body: describe the dramatic increase predicted for Japan, and compare all 3 countries in 2040.
Summary: describe 2 main things e.g. the overall trend for all 3 countries, and the biggest change that you can see.