Perhaps you should try some spelling variations:
hoang hai » hoang thi, hoang van
hang hai » hang tai, thanh hai, hang va
cua tre » cua te, cuu tre, cua triet
cac duc » cac du, cao duc, cac dac
qua cac » cua cac
sang xa » song xa, lang xa, sang ma
nang ma » tang ma, sang ma, nang cao
sai ky » sac ky
tu sai » tu bai, tu san, tu cai

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

• Performing a fuzzy search may retrieve terms with similar spellings: tu sai ky ((sang xa) or (nang ma)) hoi. hieu qua cac duc va ((hang hai) OR (hoang hai)) cua tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: tu sai ky ((sang xa) OR (nang ma)) hoi. hieu qua cac duc va ((hang hai) OR (hoang hai)) cua tre.
• The words AND, OR and NOT may confuse the search; try adding quotes: "tu sai ky ((sang xa) or (nang ma)) hoi. hieu qua cac duc va ((hang hai) OR (hoang hai)) cua tre".
• Adding a wildcard symbol may retrieve word variants: tu sai ky ((sang xa) or (nang ma)) hoi. hieu qua cac duc va ((hang hai) OR (hoang hai)) cua tre*.