Perhaps you should try some spelling variations:
thiet hach » thien hach, thuyet hach, chiet tach
thiet hai » thiet bi, thi hai, thien tai
hanh manh » hanh mang, lanh manh, hoang manh
nhung don » nhung van, nhung bo
dung cong » dung trong
manh cua » doanh cua, ban cua
bai toan » bai tap
toan ban » van ban

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

• Performing a fuzzy search may retrieve terms with similar spellings: hoc ((thiet hach) OR (thiet hai)) - hanh manh cua ((nhung don) or (dung cong)) bai toan ban~.
• If you are trying to use Boolean operators, they must be ALL CAPS: hoc ((thiet hach) OR (thiet hai)) - hanh manh cua ((nhung don) OR (dung cong)) bai toan ban.
• The words AND, OR and NOT may confuse the search; try adding quotes: "hoc ((thiet hach) OR (thiet hai)) - hanh manh cua ((nhung don) or (dung cong)) bai toan ban".
• Adding a wildcard symbol may retrieve word variants: hoc ((thiet hach) OR (thiet hai)) - hanh manh cua ((nhung don) or (dung cong)) bai toan ban*.