By which routes can insulin be administered? (Select All that Apply.)

A. Subcutaneous: Correct. The most common route for insulin administration is subcutaneous injection. B. Intradermal: Incorrect. Insulin is not administered intradermally as this route does not provide proper absorption. C. Oral: Incorrect. Insulin is not given orally because it would be broken down by digestive enzymes and stomach acid before it could be effective. D. Intravenous: Correct. Insulin can be administered intravenously in emergency situations, such as diabetic ketoacidosis. E. Topical: Incorrect. Insulin is not effective when applied topically.