RS-232 is one of the oldest and most widely used standards for serial communication, defining the voltage levels, signal timing, and mechanical connectors used to exchange data one bit at a time between two devices. Historically it linked a DTE (Data Terminal Equipment, e.g. a computer) to a DCE (Data Communication Equipment, e.g. a modem). Let us evaluate each statement.

• S1 — TRUE. The DB9 (9-pin D-subminiature) connector is the connector most commonly associated with RS-232 on PCs and equipment; the larger DB25 was the original connector before the reduced 9-pin version became standard.
• S2 — FALSE. RS-232 does not use the RJ45 modular connector for standard serial communication. The RJ45 8-pin connector is the standard for Ethernet networking (IEEE 802.3) over twisted-pair cable. (RJ45-style plugs are sometimes used in ad-hoc serial console adapters, but that is not the RS-232 standard connector.)
• S3 — TRUE. RS-232 is inherently a point-to-point interface: it connects exactly two devices (one DTE and one DCE). It is not a shared multi-drop bus like RS-485.

Since S1 and S3 are true and S2 is false, the correct choice is Only S1 and S3. The combinations that include S2 must be rejected because they treat the incorrect RJ45 claim as true, and the choice naming only S1 wrongly discards the valid point-to-point property of S3.