Type 1 diabetes is caused by destruction of beta cells in the pancreas that produce insulin. Which of the following best explains why a person with this disease needs medication?

a. Medication is needed to act as a signaling molecule to activate the signal transduction pathway.
b. Medication is needed to allow alternate signaling transduction pathways to control glucose levels.
c. Medication is needed to open channels to allow signaling molecules to enter pancreatic cells.
d. Medication is needed to serve as second messengers to regulate glucose uptake by cells.