Read the following passage and mark the letter A, B, C, or D on your answer sheet to indicate the correct answer to each of the questions from 30 to 34.

        Bitcoins are a form of virtual currency. In other words, they are a type of money that does not exist in the actual world. However, they can be used to purchase actual products and services from real companies.

        The bitcoin system was created in 2009 by an enigmatic person named Satoshi Nakamoto. In fact, no one is sure if Satoshi Nakamoto is an actual person or a group of people. Bitcoins are designed to serve as an alternative to national currencies, such as dollars and euros, They can be used to pay for things instead of cash or credit cards. When bitcoins are transferred from a buyer to a seller, the transaction is recorded in a public database.

        Governments are concerned that bitcoins can easily be stolen by hackers. It has dawned on them that they might be used for illegal purposes. For example, stolen goods could be purchased without the government's knowledge. Although more and more companies are beginning to accept bitcoins, the percentage of purchases made using bitcoins is minuscule compared to other online payment methods, such as credit cards. Instead, many bitcoin owners simply keep them as an investment since more valuable in the future.

        This may or may not be a wise approach. Currently, the value of bitcoins is fluctuating wildly, especially when compared to highly stable national currencies, Bitcoin Investors are gambling on the hope that as this high-tech money becomes more widely accepted, its value will soar.

(Adapted from: https://www.digitalcommerce360.com/)

Which of the following is defined in the passage?

A. Bitcoins

B. Transactions

C. Credit cards

D. Public Database