Fact 1: Acactus stem is used for storing water. Fact 2: Saguaro cactus grow very slowly. Given the two facts above, what is stored in the stem of the saguaro?

Available options:
1). gas;
2). water;
3). ice;
4). sand;
5). fibrous;
6). sugar;
7). glucose;
8). energy;
Answer:
2).