What kind of research design or methodology allows us to make causal conclusions by demonstrating that a change in one variable causes a change in another variable?

Which of these best describes the function of a "super pac"? a)create bi-partisan legislation that can become law b)organization meant to reign-in spending of political candidates during election cycles c)promote the interests of supreme court justices without breaking specific tampering laws d)raise funds through donations from corporations or individuals to support or oppose specific political candidates