The correct answer is B. Two.
Every business transaction affects at least two accounts: the account that is credited and the account that is debited. For example, if you buy a product from a store, the store will credit your account with the purchase amount and debit their account with the same amount.
Option A is incorrect because it is possible for a business transaction to affect more than two accounts. For example, if you sell a product to a customer, you will credit your account with the sale amount and debit your inventory account with the cost of the product. You may also need to debit accounts payable if you owe money to a supplier for the product.
Option C is incorrect because it is not always the case that a business transaction affects three accounts. For example, the transaction described above only affects two accounts.
Option D is incorrect because it is not possible for a business transaction to affect an infinite number of accounts. Every business transaction must affect at least two accounts.