c.) a public service announcement on local T.V. This is the correct option.
People from a local community , San Antonio, are in need to get the cure of a disease. The local authorities have got the cure and know people will run desperately to get it. The authorities should communicate about this cautiously and properly -timely-. A public service annoucement is used to give news for the benefit of a community. If the arrival of the cure is announced through TV, the most people will get the information.
These options are not right:
a.) a professional journal ( This will be for doctors not for ordinary people).
b.) a press release in local paper ( This is given by an important person to the paper. The authorities may give a press release to inform about the decision or the situation but the information may not be clear and accurate. Besides, a local paper is not as massive as a local TV channel)
d.) a feature column in a nationally published newspaper ( This will deal with the issue but as a comment. This will not reach the local people immediately).