Final answer:
a) Insufficient insulin production. The clinical manifestations of DM appear due to a combination of insufficient insulin production and excess insulin resistance.
Step-by-step explanation:
The clinical manifestations of diabetes mellitus (DM) appear due to a combination of factors. One of the main causes is insufficient insulin production, which occurs in type 1 diabetes (Insulin Dependent Diabetes Mellitus-IDDM). Another cause is excess insulin resistance, which is common in type 2 diabetes (Insulin Independent Diabetes Mellitus-IIDM). In type 2 diabetes, cells of the body become unresponsive to insulin, leading to elevated blood glucose levels. Therefore, options a) and b) are correct.