Explanation:

The word that names a necessary part of the underlined word "Purchase" is "Acquisition". Here's the explanation:

Definition of Purchase:
Purchase is a verb that means to acquire or obtain something by paying for it.

Understanding the Options:
Let's go through the options one by one to understand why "Acquisition" is the correct answer.

a) Trade: Trade refers to the exchange of goods, services, or commodities. While trade can be related to a purchase, it is not a necessary part of a purchase.

b) Money: Money is the medium of exchange used to buy goods or services. While money is necessary to make a purchase, it is not a part of the word "Purchase" itself.

c) Bank: A bank is a financial institution that provides various services such as deposit accounts, loans, and currency exchange. While a bank may be involved in the process of making a purchase, it is not a necessary part of the word "Purchase".

d) Acquisition: Acquisition refers to the act of acquiring or obtaining something. In the context of the word "Purchase", acquisition is a necessary part as it directly relates to obtaining something by paying for it.

Conclusion:
Among the given options, "Acquisition" is the word that names a necessary part of the underlined word "Purchase". It represents the act of obtaining something through payment, which is the essence of a purchase.