Perhaps you should try some spelling variations:
toc sach » hoc sach, doc sach, thuoc sach
cau tren » cu tren, dau tren, ca tren
sach ky » sac ky, sach y, sach ty
nang xa » nang x, lang xa, nang ma
vat dan » va dan, van dan, vat ran
dan vai » dan va, dan tai, dan vat
cua tre » cua te, cuu tre, cua triet
va nam » van nam, va nay

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 ky nang xa hoi. hieu ((va nam) OR (ha nam)) thuc vat dan vai ((cau tren) or (cua tre))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: toc sach ky nang xa hoi. hieu ((va nam) OR (ha nam)) thuc vat dan vai ((cau tren) OR (cua tre)).
• The words AND, OR and NOT may confuse the search; try adding quotes: "toc sach ky nang xa hoi. hieu ((va nam) OR (ha nam)) thuc vat dan vai ((cau tren) or (cua tre))".
• Adding a wildcard symbol may retrieve word variants: toc sach ky nang xa hoi. hieu ((va nam) OR (ha nam)) thuc vat dan vai ((cau tren) or (cua tre))*.