Answer:
D. Court clerks refusing to issue marriage licenses to same-sex couples.
Step-by-step explanation:
Grassroots is defined as: "the ordinary people in a society or an organization, especially a political party,"
The examples are mostly not about ordinary people.
California passing a proposition is about people in power.
A magazine acting as activist is a big media in action.
The supreme court is also not a representation of ordinary people.
Therefore we have court clerks refusing to do something. They're not the powerful people in court, they're employees who do some bureaucratic work. Comparing to the other examples, they're for sure ordinary people.