Patricia applied for a disability policy. On the application, she declared that she was suffering from back pains, The insurer issued the policy with an exclusion for disabilities arising from her back problems during the first twenty-six weeks. After thirty weeks, she experienced a multiple sclerosis problem. The insurer denied Patricia's claim after determining that she had received treatment for her multiple sclerosis within twelve months before the policy was issued. On which of the following clauses did the insurer have a basis for denying the claim? Select one: a. Exclusion for pre-existing medical condition b. Legal exclusion c. Exclusion for intentional concealment d. Contractual exclusion