Hi,
Je/tu dois
Il doit
Nous devons
Vous devez
Ils/elles doivent
Have a good day !!
Good luck with your studies
A = Quickly
B = Economically
C = Easily
D = A lot / Often
Si nous voulons sauver la planète, il faut que nous utilisions les ressources naturelles =
If we want to save the planet, we must use natural resources
I think the answer is B. Economically.
Si nous voulons sauver la planète, il faut que nous utilisions les ressources naturelles beaucoup.
(I apologize if this is wrong. I graduated my French unit awhile ago.)