If the complex cholesterol- HRP would not be commercially available, use the knowledge you learnt and internet to determine an alternative way for detecting cholesterol.

Classical chemical methods, enzymatic assays, gas chromatography (GC), liquid chromatography (LC), and mass spectrometry (MS)

Explanation:

Classical chemical methods, enzymatic assays, gas chromatography (GC), liquid chromatography (LC), and mass spectrometry (MS) are the alternate methods used for the detection of cholesterol. These methods are used when HRP would not be commercially available for the analysis or detection of cholesterol in the patient's body so these methods can be used for the purpose of detection of cholesterol.

well, that's easy; the answer's c, "it reduces contamination of the water and substrate of the estuary."