Perhaps you should try some spelling variations:
recent challenges » present challenges, recent changes, treatment challenges
challenges caused » challenges case, challenges chapter, challenges call
caused among » clausus among, use among, uses among
wang yang » wang yan, wang liang, wang yanling
among tai » among team, among a, among di
a recent » 1 recent, 4 recent, 3 recent
yang xi » yang di, yang yi, yang jui
ngo a » ngos a, neo a, ngo 1
ng a » lng a, png a, g 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 xi))((ng a) OR (ngo a)) a recent challenges caused among tai ;~.
• If you are trying to use Boolean operators, they must be ALL CAPS: ((wang yang) OR (yang xi))((ng a) OR (ngo a)) a recent challenges caused among tai ;*.
• The words AND, OR and NOT may confuse the search; try adding quotes: "((wang yang) or (yang xi))((ng a) OR (ngo a)) a recent challenges caused among tai ;*".