Which of the following activities will be subject to tax on unrelated business income?

a. A church's weekly bingo game. Bingo is legal in the state where the church operates and there is no commercial competition.

b. A group promoting agricultural education sells tickets to a livestock exhibition at a county fair.

c. A charity thrift store sells donated items to the general public.

d. A health education organization runs healthy-eating stands that sell fresh smoothies to the general public.