The threshold effect refers to the phenomenon of putting forward a small request before putting forward a larger request, so as to increase the possibility of others accepting a larger request.
According to the above definition, which of the followings belongs to the threshold effect?
A survey shows that 48% of urban residents are willing to donate to save endangered species. If people are asked to sign the petition for saving endangered species (almost everyone will agree to sign) and then ask them to donate, the number of people willing to donate will increase by 20%.