**Explanation:**

A hire purchase agreement is a legal contract between a buyer and a seller for the purchase of a specific asset, usually a durable good such as a car or furniture. The agreement allows the buyer to acquire the asset immediately by paying a part of the total price as a down payment, while the remaining amount is paid in installments over a specific period of time.

**1. Agreement of Sale:**
An agreement of sale is a contract where the seller agrees to sell the goods to the buyer at a future date or upon the fulfillment of certain conditions. In a hire purchase agreement, the buyer agrees to purchase the asset from the seller upon the completion of the installment payments. Therefore, a hire purchase agreement can be considered as an agreement of sale.

**2. Contract of Sale:**
A contract of sale is a legally binding agreement between a buyer and a seller for the exchange of goods or services for an agreed upon price. In a hire purchase agreement, the buyer agrees to purchase the asset from the seller by paying the installment payments. Therefore, a hire purchase agreement can be considered as a contract of sale.

**3. Bailment plus Agreement to Sell:**
Bailment refers to the transfer of possession of goods from one person (the bailor) to another (the bailee) for a specific purpose, with the goods being returned or disposed of according to the bailor's instructions. In a hire purchase agreement, the seller retains the ownership of the asset until the buyer completes the installment payments. The possession of the asset is transferred to the buyer (bailee) under a bailment arrangement, with an agreement to sell the asset upon the completion of payments. Therefore, a hire purchase agreement can be considered as a bailment plus agreement to sell.

**4. Pledge plus Agreement to Sell:**
A pledge is a legal arrangement where a person (the pledgor) gives an asset as security for a loan or debt to another person (the pledgee). In a hire purchase agreement, the buyer pledges the asset being purchased as security for the installment payments. However, the ownership of the asset is transferred to the buyer upon the completion of payments, unlike a traditional pledge arrangement. Therefore, a hire purchase agreement cannot be considered as a pledge plus agreement to sell.

Based on the above explanations, the correct answer is option 'C' - a hire purchase agreement is a bailment plus agreement to sell.