7. The logic of בית הלל is (see ר"ן): a) the husband was מפר half of the נדר, and the father now can be מפר the other half. b) the husband's ability to be מפר goes completely to the father who can be מפר alone. c) the 1st husband's ability to be מפר only weakens the נדר, which requires the father to be מפר. d) the 1st husband's ability to be מפר only weakens the נדר, and is transferred to the 2nd husband