Perhaps you should try some spelling variations:
present challenges » current challenges, assessment challenges
challenges m » challenges 1, challenges 3, challenges 5
a present » _ present, 3 present, 2 present
wang yang » wang yan, wang liang, wang yanling
zhong tai » hong tan, hong hai, zhong zhi
yang xi » yang di, yang jui
yang yi » yang di, yang jui
m zhong » 2 zhong, ji zhong, wu zhong
ya a » a a, y a, ye a

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: ((wang yang) OR (((yang xi) OR (yang yi))))ng ya a present challenges m zhong tai ;~.
• The words AND, OR and NOT may confuse the search; try adding quotes: "((wang yang) or (((yang xi) OR (yang yi))))ng ya a present challenges m zhong tai ;~".
• Adding a wildcard symbol may retrieve word variants: ((wang yang) or (((yang xi) OR (yang yi))))ng ya a present challenges m zhong tai ;*.