How Do Normal Civilians Become Domestic Terrorists, According to Vidino

How do normal civilians become domestic terrorists, according to Vidino?

A) They become radicalized by themselves though personal experiences and interactions with peers, and seek out groups like AQ or AQIM on their own.
B) When people see how politics actually work, especially in the United States, it's hard for them to restrain from violent actions against the government.
C) Extremist mosques hide under the pretense of being moderate but have programs designed to radicalize individuals.
D) Most citizens that become domestic terrorists are not actually normal and usually have a mental illness.