Perhaps you should try some spelling variations:
present challenges » current challenges, assessment challenges
challenges xia » challenges 1, challenges 3, challenges 5
3 present » _ present
zhang yan » zhang fan, zhang jian, wang yan
fang hai » dang hai, shang hai, eang hay
yang xi » yang di, yang jui
yang yi » yang di, yang jui
png a » png _, peg a
lng a » lng _, leg a, lpg a

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

• Performing a fuzzy search may retrieve terms with similar spellings: ((zhang yan) or (((yang xi) or (yang yi))))((png a) or (lng a)) 3 present challenges xia fang hai ;~.
• If you are trying to use Boolean operators, they must be ALL CAPS: ((zhang yan) OR (((yang xi) OR (yang yi))))((png a) OR (lng a)) 3 present challenges xia fang hai ;.
• Adding a wildcard symbol may retrieve word variants: ((zhang yan) or (((yang xi) or (yang yi))))((png a) or (lng a)) 3 present challenges xia fang hai ;*.