Final Answer:
The assay can be used to determine the expression of enzyme under different environmental conditions. If the gene is expressed and the substrate is present, d) the enzyme will be broken down and create a color pigment.
Step-by-step explanation:
The key to the correct answer lies in understanding the process described in the question. The assay aims to determine the expression of a gene under different environmental conditions.
d) Enzyme: The correct answer. The expression of the gene is related to the production of the enzyme. If the gene is expressed, the enzyme is produced.
If the gene is expressed and the substrate is present, d) the enzyme will be broken down and create a color pigment.