Here's the correct sequence of levels of organization in a human, from simplest to most complex:

1. Cells: The basic unit of life. Examples include muscle cells, nerve cells, and blood cells.

2. Tissues: Groups of similar cells working together to perform a specific function. Examples include muscle tissue, nervous tissue, and connective tissue.

3. Organs: Structures made up of different tissues that work together to perform a specific function. Examples include the heart, lungs, and stomach.

4. Organ Systems: Groups of organs that work together to perform a major function. Examples include the circulatory system, respiratory system, and digestive system.

5. Organism: A complete living being made up of all the organ systems working together. In this case, a human being.

Let me know if you'd like more detail on any of these levels!