单选题 Only recently ______ to realize the dangers caffeine (咖啡因) might bring to our health.
A. that scientists began B. have scientists begun
C. scientists have begun D. that did scientists begin

【正确答案】 B

【答案解析】[解析] so，often，only等表示程度或频率的副词置于句首时，句子需部分倒装。将be动词、助动词或情态动词提到主语前。此题中，only被置于句首，因此，应将助动词have提前。这样得出正确选项B。