Which action is a form of grassroots activism that supported or opposed
same-sex marriage?
O
A. President Barack Obama appointing a transgender woman to his
cabinet
O
B. Bakery owners refusing to make cakes for same-sex couples
O
C. The Supreme Court ruling that the Defense of Marriage Act is
unconstitutional
O
D. The magazine One publishing material aimed at a gay audience

B. Bakery owners refusing to make cakes for same-sex couples

Explanation:

Grassroots activism is at a local level, which eliminates C.

Publishing for an audience isn't necessarily supporting or opposing them, not is it at a local level- eliminating D.

As for A, being transgender doesn't relate to same-sex marriage, and President Obama appointing someone to the cabinet isn't considered local either.

I hope this helped!