Which types of credit are most similar to eachother?

The correct answer is: "auto loan and mortgage loan"
Both are secured types of credit, loans which are granted by a financial instution to a borrower, under the condition that the latter provides a guarantee that proves his ability of returning the funds. Such proof is materialized through the provision an asset that the bank would keep in case of default (a collateral).
A mortgage is a secured debt instrument which is granted by financial institutions and demanded by borrowers who aim to buy a real state property.  In fact, such property works as collateral and, in the case of default in montly repayments, the financial institution that provided the credit has the right to own the property in return. The auto loan functions exactly in the same way, but instead of buying a real state property, it is used to finance the purchase of a car. The car would work as collateral in case of default.

Read more on -

The answer would be option a , b, and c.