The section presents a question related to the composition of water, specifically asking which element is the main component. The options provided are:

A. Oxy (Oxygen)  
B. Hydro (Hydrogen)  
C. Canxi (Calcium)  
D. Natri (Sodium)  

Key topics include the chemical composition of water and the identification of its primary elements. The main entities involved are the elements oxygen and hydrogen, which are essential for understanding the structure of water (H2O).