The Transfer of Property Act, 1882, distinguishes between vested and contingent interests.
\[\begin{array}{rl} \bullet & \text{**Vested Interest (S. 19):** An interest is vested when it is not dependent on an uncertain event. The enjoyment may be postponed, but the title is already conferred. The event on which it depends is a certain event, like death or the passage of time.} \\ \bullet & \text{**Contingent Interest (S. 21):** An interest is contingent when it depends on the happening or not happening of a specified uncertain event.} \\ \end{array}\]
In options (A), (B), and (D), the transfer depends on events that are certain to happen (death, passage of time). In option (C), the transfer depends on 'C' marrying 'B', which is an uncertain event—it may or may not happen. Therefore, this creates a contingent interest, not a vested one.