A nurse is teaching diabetic clients about the use of insulin. For which of the following types of insulin should the nurse tell the clients to expect an onset of 15 to 30 minutes?

A. Insulin glargine (Lantus): This is a long-acting insulin, with no pronounced peak and a slow onset, typically around 1-2 hours. B. Glucagon (Glucagen): This is not an insulin; it's used to treat severe hypoglycemia. C. Glipizide (Glucotrol): This is an oral medication used to stimulate insulin secretion, not an insulin itself. D. Insulin lispro (Humalog): Insulin lispro is a rapid-acting insulin with an onset of 15 to 30 minutes.