Creating better health care, education and housing for everyone is a simple idea, but which is hard to put into practice．
A. one
B. that
C. the one
D. the other
网友回答
(答案→)A. one
B. that
C. the one
D. the other
解析：考查代词。本空代词作前面的a simple idea的同位语，都是第一次提到，因此用代词one。