A scientist cooled a sample of a pure liquid substance and recorded its temperature over time.
From A to B the substance is a liquid. From C to D the substance is a solid.
| Time (minutes) | Temperature (°C) | Point |
|---|---|---|
| 0.0 | 150 | A |
| 4.5 | 65 | B |
| 11.5 | 65 | C |
| 17.5 | 20 | D |
State the time when the liquid first started to freeze.
