28. 다음 글의 밑줄 친 부분 중, 어법상 틀린 것은? [3점] Psychologists who study giving behavior ① have noticed that some people give substantial amounts to one or two charities, while others give small amounts to many charities. Those who donate to one or two charities seek evidence about what the charity is doing and ② what it is really having a positive i..