The right answer is B. A law banning all automatic and semiautomatic firearms.
The second amendment states: A well regulated Militia, being necessary to the security of a free State, the right of the people to keep and bear Arms shall not be infringed. The law is divided in two pieces. The first one is related with the need of a state security, in this case militia, to protect the security of the citizens. And the second part, is related with the inalienable right of people to keep and bear firearms, as one tools against aggressors and tyrannical government. A law imposing restrictions to the right of bear firearms would be in total opposition of the second amendment.