Histocompatibility antigens that attack foreign tissue in the body cannot have been selected through evolution expressly to ______________ organ transplantation; on the contrary, they have been found to facilitate many essential biological functions.
1. enhance
2. retain
3.thwart
4. obviate
5. hurdle
답은 3 thwart 인데, 왜 obviate은 답이 안되는지 궁금합니다.
facilitate 의 반대인, 막다의 뜻으로 blank를 넣어야 하는게 아닌가요?