Perhaps you should try some spelling variations:
hieu van » hieu va, thien van, lieu va
toc sach » hoc sach, doc sach, thuoc sach
van hanh » van thanh, ban hanh, van anh
vai cua » dai cua, hai cua, lai cua
van cac » van hac, van cau, van bac
ty nang » ky nang, ty xang, ty hang
nang o » nang co, nang ho, nang ro
cac bo » bac bo, cac co
bo van » vo van, so van, do van
vi cua » di cua
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: ((te sach) OR (toc sach)) ty nang o hai. hieu van cac bo van hanh ((vi cua) or (vai cua)) tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: ((te sach) OR (toc sach)) ty nang o hai. hieu van cac bo van hanh ((vi cua) OR (vai cua)) tre.
• The words AND, OR and NOT may confuse the search; try adding quotes: "((te sach) OR (toc sach)) ty nang o hai. hieu van cac bo van hanh ((vi cua) or (vai cua)) tre".
• Adding a wildcard symbol may retrieve word variants: ((te sach) OR (toc sach)) ty nang o hai. hieu van cac bo van hanh ((vi cua) or (vai cua)) tre*.