Consider the following statements about errors:

1. If the absolute error in length is $\pm 0.5$ mm, the same error is more serious for a length of 1 mm than for a length of 1 m.
2. Relative error has no unit.
3. The reliability of a result increases when the accuracy is reported with the result.

• ai and ii
• bi and iii
• cii and iii
• di, ii and iii