Under the Code of Civil Procedure, 1908, Order XX Rule 2 relates to which of the following?

Under Section 113 of the CPC, a Reference can be made to the High Court during the pendency of a case when:

The purpose of ________ is to enable subordinate courts to obtain, in non-appealable cases, the opinion of the High Court on a question of law and thereby avoid the commission of an error which could not be remedied later.