Study the table below, which shows the change in employment structure for an emerging economy between 1970 and 2020.
| Year | Primary industry (%) | Secondary industry (%) | Service industry (%) |
|---|---|---|---|
| 1970 | 42 | 20 | 38 |
| 1980 | 33 | 24 | 43 |
| 1990 | 25 | 27 | 48 |
| 2000 | 21 | 29 | 50 |
| 2010 | 19 | 27 | 54 |
| 2020 | 18 | 25 | 57 |
Which one of the following describes the change in employment in primary industry from 1970 to 2020?
It stays the same
It more than halves
It halves
It doubles
