Perhaps you should try some spelling variations:
vien cac » vien bach, vien dai, vien da
toc sach » hoc sach, doc sach, thuoc sach
hanh doi » thanh doi, hanh noi, hang doi
doi cuu » doi cua, doi cuoc
va hanh » van hanh, va thanh, va danh
cuu tre » cua tre, cau tren, cau treo
nang ma » tang ma, sang ma, nang cao
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: ((te sach) or (toc sach)) ky nang ma hoa. hieu ((ve cac) OR (vien cac)) nuoc va hanh doi cuu tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: ((te sach) OR (toc sach)) ky nang ma hoa. hieu ((ve cac) OR (vien cac)) nuoc va hanh doi cuu tre.
• The words AND, OR and NOT may confuse the search; try adding quotes: "((te sach) or (toc sach)) ky nang ma hoa. hieu ((ve cac) OR (vien cac)) nuoc va hanh doi cuu tre".
• Adding a wildcard symbol may retrieve word variants: ((te sach) or (toc sach)) ky nang ma hoa. hieu ((ve cac) OR (vien cac)) nuoc va hanh doi cuu tre*.