(4)Where the property referred to in sub-section (2) consists of more than one house-(a)the provisions of that sub-section shall apply only in respect of one of such houses, which the assessee may, at his option, specify in this behalf;(b)the annual value of the house or houses, other than the house in respect of which the assessee has exercised an option under clause (a), shall be determined under sub-section (1) as if such house or houses had been let.]