1) Can you identify the one that is not appropriate?
The line graph on the left/shown is not appropriate.
2) Why do you think it's not appropriate?
A line graph is to show something changing over a period of time but the information given is at that time and not over a period of time.
3) What makes you think the 3 remaining graphs are appropriate?
The 3 remaining graphs show the information at that time and not over a period of time.