Meilleure réponse !
2) Wrong: 'I have spent thousand of hours in  my plane observing wolves"

3)Wrong : "I went to Nothern Canada, to an island hundreds of miles north of Hudson Bay. Arctic wolves live there, more than a thousand miles from the nearest city."

4) Right : 'I've done something no one has ever done before"

5)Wrong : 'I was always very careful not to frighten them."

6)Wrong : "This is the first time a man has ever actually lived with a pack of wolves. 

Voilà!! :)