D. OPV can spread to individuals who were missed in the vaccination program and thereby immunize them also.

This can and does occur. And although the spread of the vaccine virus from vaccinees to unvaccinated persons may sometimes result in the development of a cVDPV, most of the time it causes asymptomatic infections that are immunizing. Because the vaccine may spread in this way, there is less concern that every single individual in a country will need to receive vaccination in order for polio eradication to be achieved.

This is a bonus for the eradication programs, but it does not explain why OPV is necessary to achieve eradication and why IPV is not just as good. Try another answer.