Answer:
A. Gene expression
Step-by-step explanation:
Every cell has the same DNA, but because of gene expression, we have different cells in our bodies.
Gene expression turns specific genes on and off, which makes each cell have a unique function with differences in things such as protein types.
Gene expression also leads to different cells in our bodies because it changes the function of certain cells.
For example, red blood cells and white blood cells have different functions because of different gene expressions.
So, A is correct.