Perhaps you should try some spelling variations:
cau tren » cu tren, dau tren, ca tren
thuc dan » thuc hanh, hoc dan, thuc vat
thuc va » thuc vat, thuc day
tu sach » thu sach, te sach, tu cach
hieu ve » hieu va, hieu van
cao hoi » cau hoi, co hoi, cao hoc
su sach » so sach, vu sach
ca cau » cua cau, cac cau, can cau
ve cac » va cac, vien cac

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

• If you are trying to use Boolean operators, they must be ALL CAPS: ((tu sach) OR (su sach)) ky nang cao hoi. hieu ve cac ((thuc va) OR (thuc dan)) dan ca cau tren~.
• The words AND, OR and NOT may confuse the search; try adding quotes: "((tu sach) or (su sach)) ky nang cao hoi. hieu ve cac ((thuc va) OR (thuc dan)) dan ca cau tren~".
• Adding a wildcard symbol may retrieve word variants: ((tu sach) or (su sach)) ky nang cao hoi. hieu ve cac ((thuc va) OR (thuc dan)) dan ca cau tren*.