The table shows the melting points and boiling points of four substances: P, Q, R, and S.
| Substance | Melting point in °C | Boiling point in °C |
|---|---|---|
| P | −114 | 78 |
| Q | 44 | 280 |
| R | 186 | 357 |
| S | −183 | −161 |
Using the information in the table, give the letter of the substance that is a liquid at 120 °C.