Perhaps you should try some spelling variations:
main challenges » remaining challenges
challenges time » challenges jaime, challenges third, challenges trust
time cheng » time change, time when, time changes
yang yang » wang yang, wang yan
yang jin » yang jie, yang jun, ying jin
cheng lu » cheng chu, chen yu, cheng _
yang yi » yang xi, yang jui

You may be able to get more results by adjusting your search query.

• If you are trying to use Boolean operators, they must be ALL CAPS: yang yang ((((yang jin) OR (yang di))) OR (yang yi)) main challenges time cheng lu ;~.
• Adding a wildcard symbol may retrieve word variants: yang yang ((((yang jin) or (yang di))) or (yang yi)) main challenges time cheng lu ;*.