Perhaps you should try some spelling variations:
recent challenges » present challenges, recent changes, treatment challenges
challenges may » challenges m, challenges small, challenges moral
four recent » our recent
wang yang » wang yan, wang liang, wang yanling
zhong zhi » zhang zhi, zhong tai
hong ghi » hong g, hong hai
ng a » lng a, ngo a, png a

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

• Performing a fuzzy search may retrieve terms with similar spellings: ((wang yang) or (yang di))ng a four recent challenges may ((zhong zhi) or (hong ghi)) ;~.
• If you are trying to use Boolean operators, they must be ALL CAPS: ((wang yang) OR (yang di))ng a four recent challenges may ((zhong zhi) OR (hong ghi)) ;.
• Adding a wildcard symbol may retrieve word variants: ((wang yang) or (yang di))ng a four recent challenges may ((zhong zhi) or (hong ghi)) ;*.