A Researcher Believes That the Foot-In-The-Door Effect, Rather Than the Lowballing

A researcher believes that the foot-in-the-door effect, rather than the lowballing tactic, is what primarily gets a person to agree to donate money to a charity after initially only agreeing to sign a petition in support of the charity's cause. How might the researcher definitively test between these two theoretical accounts?

A) by asking participants why they felt like it was a good idea to donate money to the charity
B) by comparing a condition in which participants first sign a petition and then are asked to donate money to a condition in which the order of these procedures is reversed
C) by asking participants to complete a self-related attitudes scale after they sign the petition and before they are asked to donate money
D) by randomly assigning participants to either sign the petition or donate money, and assessing which approach leads to greater support for the cause