Perhaps you should try some spelling variations:
tu sach » thu sach, su sach, te sach
thuc va » thuc vat, thuc dan, thuc day
truc va » thuc vat, trung va
cua tre » cua te, cuu tre, cua triet
hieu ve » hieu va, hieu van
mai hoi » mai khoi, dai hoi, lai hoi
ky sang » ky dang, ky tang, duy sang
vi cua » vai cua, di cua
ve cam » ve cham, ve cac, va cam

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 ((ky sang) or (ky nang)) mai hoi. hieu ve cam ((truc va) OR (thuc va)) hanh vi cua tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: tu sach ((ky sang) OR (ky nang)) mai hoi. hieu ve cam ((truc va) OR (thuc va)) hanh vi cua tre.
• The words AND, OR and NOT may confuse the search; try adding quotes: "tu sach ((ky sang) or (ky nang)) mai hoi. hieu ve cam ((truc va) OR (thuc va)) hanh vi cua tre".
• Adding a wildcard symbol may retrieve word variants: tu sach ((ky sang) or (ky nang)) mai hoi. hieu ve cam ((truc va) OR (thuc va)) hanh vi cua tre*.