Perhaps you should try some spelling variations:
toc sach » hoc sach, thuoc sach, nuoc sach
doc sach » hoc sach, nuoc sach, dac sac
ban hanh » ban hang
van hanh » van thanh, van anh, van ban
tai cua » thai cua, tai cuc, tri cua
hieu ve » hieu va, hieu van
nang ma » tang ma, sang ma, nang cao
ly nang » ky nang, ly hang, ly vang
cua tre » cua te, cuu tre, cua triet
ve dat » de dat, va dat, ve dao

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)) ly nang ma hoa. hieu ve dat nuoc ((van hanh) or (ban hanh)) tai cua tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: ((toc sach) OR (doc sach)) ly nang ma hoa. hieu ve dat nuoc ((van hanh) OR (ban hanh)) tai cua tre.
• The words AND, OR and NOT may confuse the search; try adding quotes: "((toc sach) OR (doc sach)) ly nang ma hoa. hieu ve dat nuoc ((van hanh) or (ban hanh)) tai cua tre".
• Adding a wildcard symbol may retrieve word variants: ((toc sach) OR (doc sach)) ly nang ma hoa. hieu ve dat nuoc ((van hanh) or (ban hanh)) tai cua tre*.