题目

 Thank you for the great difficulty you have had ______ me with my designing work．    A． helping            B.  to help        C．with helping     D．to have helped 答案：A在人口增长模式转变过程中，先转变的是 (　　)A. 出生率 B. 死亡率 C. 自然增长率 D. 生育率