Which two structures produce energy that cells can use?

To provide an accurate answer, I would need to know what structures A, B, C, and D refer to. However, in biological terms, if you are asking about structures that produce energy that cells can use, typical structures are:

1. Mitochondria - known as the powerhouse of the cell, responsible for producing ATP, the energy currency of the cell.
2. Chloroplasts - in plant cells, these structures perform photosynthesis to convert light energy into chemical energy stored in glucose.

If you can clarify what A, B, C, and D refer to, I can help you determine which two structures produce energy for cells.