A discretionary account is the correct account type when a customer authorizes a registered representative to make investment decisions and determine when trades should be placed. Discretion means the representative has authority over one or more essential elements of the trade, such as the security, action, amount, or timing, depending on the authority granted. Choice D is correct because the question states that the representative will make investment decisions and decide when to place trades. A margin account allows the customer to borrow funds from the broker-dealer to purchase securities, but margin authority is not the same as trading discretion. An options account permits options trading after approval and risk disclosure, but it does not automatically authorize the representative to make decisions. A custodial account is opened for a minor or legally incapacitated person and managed by a custodian. The SIE outline includes discretionary versus non-discretionary accounts, customer account types, order authorization, and FINRA Rule 3260 governing discretionary accounts. Written customer authorization and firm approval are required for discretionary authority. Reference: Section 3.2.1 Account Types and Characteristics; FINRA Rule 3260 Discretionary Accounts.