Perhaps you should try some spelling variations:
toc sach » hoc sach, doc sach, thuoc sach
dan dien » doan dien, danh dien, dan den
dien cua » dieu cua, dien cuc, dien cu
nang o » nang co, nang ho, nang ro
va lam » van lam
va lap » va dap
va dan » ca dan, va dao, va dau
cua te » cua tu
o hoi » co hoi, o hoc, o hai

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