2009 California Code of Civil Procedure - Section 2030.410 :: Article 3. Use Of Interrogatory Answer

2030.410.  At the trial or any other hearing in the action, so far
as admissible under the rules of evidence, the propounding party or
any party other than the responding party may use any answer or part
of an answer to an interrogatory only against the responding party.
It is not ground for objection to the use of an answer to an
interrogatory that the responding party is available to testify, has
testified, or will testify at the trial or other hearing.