Which of the following doses of prednisolone is equivalent

Which of the following doses of prednisolone is equivalent in its glucocorticoid potency to 20 mg of
hydrocortisone?

2 mg
5 mg  This is the correct answer
10 mg
15 mg
20 mg

It is important to know the relative potencies of the glucocorticoids.
Dexamethasone for instance is roughly 30 times more potent than hydrocortisone.