Human tissues are mainly composed of

Human tissues are primarily composed of water, which constitutes about 60% to 75% of the human body, depending on factors such as age and body composition. Water is vital for various physiological functions, including temperature regulation, nutrient transport, and waste elimination.

In terms of the composition of cells and tissues, water serves as a solvent and medium for biochemical reactions, making it essential for metabolic processes. Additionally, water contributes to the structure of cells, as it helps maintain cell shape and supports various cellular activities.

While oxygen, hydrogen, and iron are also important elements found in the body (with oxygen being a critical component of water and involved in cellular respiration, hydrogen being part of many biological molecules, and iron being essential for oxygen transport in the blood), they are not present in the same abundant quantities as water. The predominance of water in human tissues is what makes it the correct answer in this context.