Considering the available options, the reason most movements use acts of civil disobedience as a last resort is that "they always lead to riots, which presents a physical risk to protestors."
Civil Disobedience is a socio-political term used to describe the individual's resistance to obey the demands of a government or to occupy power without creating any form of violence.
Usually, Civil disobedience is in protest or non-cooperation from the people to force compromises from the government.
However, given the nature of civil disobedience, like protest, they often lead to riots, which presents a physical risk to protestors.
Hence, in this case, it is concluded that the correct answer is option A.
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