Which of the following is a standard collective action problem that must be overcome for an interest group to promote or defend a shared interest?

a. there is a constitutional prohibition on unauthorized group activity.
b. The inability to communicate on a large-scale basis because of the size of the country increases the coordination problems.
c. Conformity costs are exceedingly low for such an activity, but the transaction costs of agreeing on goals can be quite high.
d. Rational self-interest leads to universal free riding, which dooms the organization as well as the effort unless some way can be found around this difficulty.

d. Rational self-interest leads to universal free riding, which dooms the organization as well as the effort unless some way can be found around this difficulty.