Fact 1: Acactus stem is used for storing water.

Fact 2: H2O is the scientific name for water.

Given the two facts above, answer the question "what can a cactus stem store?" with the following options: 
- hydrogen
 - CO2
 - h2o
 - H20
 - O2
 - liquid gold
 - thorns
 - rain


 

   h2o      