何为林木种苗“一签四证”？
参考答案：
“一签”指种苗标签。
“四证”指林木种苗生产许可证、林木种苗经营许可证、林木种苗质量检验证、森林病虫害检验证。
So difficult _____ it to live in an English-speaking country that I determined to learn English well. [ ]
A. I did feel
B. did I feel
C. I have felt
D. have I felt
六月中旬，在江淮流域，细雨连绵长达一个月之久，此时正值梅子黄熟季节，因此人们称之为"（）"。
