Perhaps you should try some spelling variations:
toc sach » hoc sach, thuoc sach, nuoc sach
cac nuoc » cap nuoc, hoc nuoc, dat nuoc
cau tren » dau tren, ca tren, cau treo
doc sach » hoc sach, nuoc sach, dac sac
hanh doi » thanh doi, hanh noi, hang doi
va hanh » van hanh, va thanh, va danh
cu tren » tu tren, dua tren
hieu ve » hieu va, hieu van
nang ma » tang ma, sang ma, nang cao
y nang » ky nang, ly nang, v nang
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: ((toc sach) or (doc sach)) y nang ma hoa. hieu ve cac nuoc va hanh doi ((cau tren) OR (cu tren))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: ((toc sach) OR (doc sach)) y nang ma hoa. hieu ve cac nuoc va hanh doi ((cau tren) OR (cu tren)).
• The words AND, OR and NOT may confuse the search; try adding quotes: "((toc sach) or (doc sach)) y nang ma hoa. hieu ve cac nuoc va hanh doi ((cau tren) OR (cu tren))".
• Adding a wildcard symbol may retrieve word variants: ((toc sach) or (doc sach)) y nang ma hoa. hieu ve cac nuoc va hanh doi ((cau tren) OR (cu tren))*.