[A] When there are more than one approval rules added, the default option can be used.

[B] When a rule is set as default, it means that whenever there is a case that more than one rule can be applied, the default rule will be applied.

[C] For example in this case, if the amount comes to be 8000, the first rule will be applied as it is set as default. 

Keyword: default rule, the default option in approval rule, default approval rule