Which of the following statements correctly describes the process of insulin secretion?

• A. Insulin is secreted by liver cells in response to fasting.
• B. Insulin is secreted by pancreatic beta cells in response to a meal, starting from its inactive precursor form, proinsulin.
• C. Insulin is secreted by adipose tissue in response to cold temperatures.
• D. Insulin is secreted by muscle cells during exercise.

Answer: (B)