单选题 ______ fairly recently that this problem was solved, at least partially.
A. Until B. Not until
C. It was until D. It was not until

【正确答案】 D
【答案解析】[解析] 本题是考查强调句，将含有not...until的一般陈述句变为强调时间状语的强调句时，需将否定词not与until一起提到强调结构中去。