A party against whom an answer has been filed may object, by demurrer as provided in Section 430.30, to the answer upon any one or more of the following grounds:
(a) The answer does not state facts sufficient to constitute a defense.
(b) The answer is uncertain. As used in this subdivision, “uncertain” includes ambiguous and unintelligible.
(c) Where the answer pleads a contract, it cannot be ascertained from the answer whether the contract is written or oral.