Final answer:
Glucose and choline are transported across the blood-brain barrier, utilizing specific transport mechanisms, while hydrogen ions are typically not allowed to pass through this selective barrier.
Step-by-step explanation:
The question relates to which substances are transported across the blood-brain barrier (BBB). The BBB is a selective permeability barrier that allows specific types of molecules to enter the central nervous system (CNS). Among the substances that can cross the BBB, glucose is notably allowed, as it is the primary energy source for the brain. Additionally, choline, a precursor for the neurotransmitter acetylcholine, can also cross the BBB through transporter proteins.
Hydrogen ions, on the other hand, do not readily cross the BBB and thus the movement of hydrogen ions across a mitochondrial membrane does not apply in this context. Based on this, the correct answer to which substances are transported across the blood-brain barrier is both A (glucose) and C (choline).