People go to clean graves and light incense their ancestors.
A. in debt
B. in their turn
C. in memory of
D. in time
网友回答
A. in debt
B. in their turn
(答案→)C. in memory of
D. in time
解析：考查介词短语：A. in debt 欠债B. in their turn轮到他们C. in memory of为了纪念D. in time及时，句意：人们打扫墓碑，燃起香纪念祖先。选C。