Perhaps you should try some spelling variations:
cac thoi » cac toi, cac hop, cac tro
tu sach » thu sach, su sach, te sach
thoi va » hoi va, thai va, tho va
cua tre » cua te, cuu tre, cua triet
hieu ve » hieu va, hieu van
tu lanh » tu hanh, tu lenh, tu manh
tu lang » cu lang, xu lang, tu quang
dan vi » doan vi, don vi, dan va
ve cac » va cac, vien cac

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

• Performing a fuzzy search may retrieve terms with similar spellings: tu sach ((tu lang) OR (tu lanh)) xa hoi. hieu ve cac thoi va ((dan vi) or (hoang thi)) cua tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: tu sach ((tu lang) OR (tu lanh)) xa hoi. hieu ve cac thoi va ((dan vi) OR (hoang thi)) cua tre.
• The words AND, OR and NOT may confuse the search; try adding quotes: "tu sach ((tu lang) OR (tu lanh)) xa hoi. hieu ve cac thoi va ((dan vi) or (hoang thi)) cua tre".
• Adding a wildcard symbol may retrieve word variants: tu sach ((tu lang) OR (tu lanh)) xa hoi. hieu ve cac thoi va ((dan vi) or (hoang thi)) cua tre*.