Nucleus (C) manages, mitochondria (A) produces energy, chloroplasts (B) act like solar panels, and endoplasmic reticulum (D) transports materials.
Consider the cell as a bustling factory where many components perform distinct functions.
With all the power, the nucleus (C) is akin to the manager's office. The energy-producing power plants are called mitochondria (A).
The solar panels that turn light into food (photosynthesis) are called chloroplasts (B), and they are mostly found in plant cells.
The transport system, or endoplasmic reticulum (D), is responsible for transferring items like a conveyor belt. Every component is essential to the factory's (cell's) smooth operation.
In other words, if you were in this factory of cells, you would see these numbers (organelles) and know what each one did, just like you would know the various machinery in a real industry.