You are presented with the quiz "what do some plants use waxy leaves for?" But you don't know the answer, so you turn to your teacher to ask for hints. He says that "waxy leaves are used for storing water by some plants" and "plants have many adaptations for conserving water or storing it". So, what's the best answer to the question?

Available choices:
(1). staying warm;
(2). petals;
(3). nutrients;
(4). Chemical energy;
(5). Exfoliation;
(6). carbon monoxide;
(7). water conservation;
(8). water evaporation;
The answer is:
(7).