Which of the following is not a ground for divorce under the Dissolution of Muslim Marriage Act, 1939 ?

The Dissolution of Muslim Marriage Act, 1939 lists cruelty, the husband's whereabouts being unknown for four years and his insanity for two years as grounds, but imprisonment is a ground only where the sentence is seven years or upwards, so "The Husband has been sentenced to imprisonment for a period of two years or upwards." is not a ground.