--You’ve made great progress in your studies of English, haven’t you? --Yes, but much .
A. remains to do
B. is remained to do
C. remains to be done
D. is remained to be done
网友回答
A. remains to do
B. is remained to do
(答案→)C. remains to be done
D. is remained to be done
解析： remain作系动词用，本身不用于被动语态，有时与不定式的被动结构构成合成谓语，意为尚待。