问题
选择题
China's population is expected to increase to about 1.5 billion in 2040, ______it will start to decline slowly.
A．where
B．which
C．on which
D．after which
答案
答案：D
题目分析：考查非限制性定语从句。句中有逗号，说明是非限制性定语从句，先行词是2040，指时间，排除A；on when相当于when，但on指具体的一天，这里的2040年是一段时间，排除C；which作主语或宾语，it will start to decline slowly不缺少成分，排除B，after which相当于after 2040，故选D。
