D.C. Code § 34-907
Every public utility shall furnish to the Commission all information required by it to carry into effect the provisions of this subtitle, and shall make specific answers to all specific questions submitted by the Commission. Any public utility receiving from the Commission any blanks with directions to fill the same shall cause the same to be properly filled out so as to answer, fully and correctly, each question therein propounded, and in case it is unable to answer any question it shall give a good and sufficient reason for such failure; and said answer shall be verified under oath by the president, secretary, superintendent, or general manager of such public utility, and returned to the Commission at its office within the period fixed by the Commission. Whenever required by the Commission, every public utility shall deliver to the Commission any or all maps, profiles, contracts, reports of engineers, and all documents, books, accounts, papers, and records, or copies of any or all of the same, with a complete inventory of all its property, in such form as the Commission may direct.
D.C. Code § 34-907