Perhaps you should try some spelling variations:
vien cac » vien bach, vien dai, vien da
thanh va » thanh van, hanh va, thanh ha
toc sach » hoc sach, doc sach, thuoc sach
va thanh » gia thanh, ban thanh, va tinh
tang van » dang van, hoang van, trong van
tu sach » thu sach, su sach, te sach
thuc va » thuc vat, thuc dan, thuc day
cua tre » cua te, cuu tre, cua triet
van hoi » van hoa, van hoc, van hoe
ky tang » ky nang, ky dang, kho tang
va cua » va chua, via cua, ca cua
ve cac » va 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) or (toc sach)) ky tang van hoi. hieu ((ve cac) OR (vien cac)) thuc va thanh va cua tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: ((tu sach) OR (toc sach)) ky tang van hoi. hieu ((ve cac) OR (vien cac)) thuc va thanh va cua tre.
• The words AND, OR and NOT may confuse the search; try adding quotes: "((tu sach) or (toc sach)) ky tang van hoi. hieu ((ve cac) OR (vien cac)) thuc va thanh va cua tre".
• Adding a wildcard symbol may retrieve word variants: ((tu sach) or (toc sach)) ky tang van hoi. hieu ((ve cac) OR (vien cac)) thuc va thanh va cua tre*.