The correct answer is clearing corporations because they perform the clearing and settlement function after a trade is executed. In securities markets, execution and settlement are distinct. An exchange or trading venue may facilitate execution by matching orders, while a clearing corporation helps ensure that the buyer receives securities and the seller receives payment according to required settlement procedures. Clearing corporations reduce operational and counterparty risk by standardizing obligations and coordinating settlement through clearing systems. Market makers provide liquidity by quoting prices, but their role is trading, not settlement administration. Investment advisers are fiduciary advisory professionals and are not involved in clearing customer trades. Exchanges are important market centers but are not the party specifically responsible for ensuring trade settlement. The SIE outline lists depositories and clearing corporations as market participants and includes DTCC and OCC as examples. It also lists trade settlement as a separate tested area, including settlement time frames and physical versus book-entry delivery. This confirms that the answer is D. Reference: Section 1.1.4 Market Participants and Their Roles; Section 3.1.3 Trade Settlement.