单选题 In the flint decades of the twentieth century, the individual gem could not be seen, but could be worked with fruitfully.
A. blindly B. completely C. productively D. carefully

【正确答案】 C

【答案解析】blindly盲目地，摸索地。completely十分地，完全地。productively有结果地，有成果地。carefully小心地，谨慎地。fruitfully产量多地，肥沃地。