Perhaps you should try some spelling variations:
toc sach » hoc sach, doc sach, thuoc sach
hieu van » hieu va, thien van, lieu va
lam duoc » nam duoc, luat duoc, lam thuoc
van lam » van nam
ma danh » va danh, mo danh, dia danh
nang o » nang co, nang ho, nang ro
ma dan » mat dan, mua dan, ca dan
di cua » dai cua, doi cua, de cua
cua te » cua tu
o hai » co hai, so hai, o lai

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 (thu hoach)) ky nang o hai. hieu van lam duoc ((ma danh) OR (ma dan)) di cua te~.
• If you are trying to use Boolean operators, they must be ALL CAPS: ((toc sach) OR (thu hoach)) ky nang o hai. hieu van lam duoc ((ma danh) OR (ma dan)) di cua te.
• The words AND, OR and NOT may confuse the search; try adding quotes: "((toc sach) or (thu hoach)) ky nang o hai. hieu van lam duoc ((ma danh) OR (ma dan)) di cua te".
• Adding a wildcard symbol may retrieve word variants: ((toc sach) or (thu hoach)) ky nang o hai. hieu van lam duoc ((ma danh) OR (ma dan)) di cua te*.