Answer:
Supporting us in the fact that fossil ferns have been found in Canada, we can conclude that: Canada once had a much warmer climate.
Explanation:
To understand this answer we need to analyze all the options.
1.- Canada once had a much warmer climate. This is correct because ferns only grow in environments with 73 and 86 Fahrenheit grades. Today Canada's temperature from 20 to almost 60 in general.
2.- Giant dragonflies once lived in Canada. Well, we can say that because we don't have information about dragonflies in our information. So it's incorrect.
3.- Canada was once covered by a giant sea. Well, we can't say that based on the information in the phrase. So it's incorrect.
4.- Dinosaurs once lived in Canada. The paragraph doesn't provide relevant information about dinosaurs, so it's incorrect.