Perhaps you should try some spelling variations:
hoc sach » hoc sinh, hoc cac, hoc anh
nam thuc » nam thuoc, am thuc, nam thu
toc sac » toc sach, toc san, doc sach
ky lang » ky dang, ky tang, tay lang
hieu va » lieu va, hieu qua
thuc va » thuc vat, thuc dan, thuc day
dan vai » dan va, dan tai, dan vat
vai cau » va cau, van cau, vai cac
va nam » van nam, ha nam, va nay
va dan » ca dan, va dao, va dau

You may be able to get more results by adjusting your search query.

• Performing a fuzzy search may retrieve terms with similar spellings: ((toc sac) or (hoc sach)) ((ky lang) OR (ky nang)) xa hoi. hieu va nam thuc va dan vai cau tao~.
• If you are trying to use Boolean operators, they must be ALL CAPS: ((toc sac) OR (hoc sach)) ((ky lang) OR (ky nang)) xa hoi. hieu va nam thuc va dan vai cau tao.
• The words AND, OR and NOT may confuse the search; try adding quotes: "((toc sac) or (hoc sach)) ((ky lang) OR (ky nang)) xa hoi. hieu va nam thuc va dan vai cau tao".
• Adding a wildcard symbol may retrieve word variants: ((toc sac) or (hoc sach)) ((ky lang) OR (ky nang)) xa hoi. hieu va nam thuc va dan vai cau tao*.