Perhaps you should try some spelling variations:
vien cac » vien bach, vien da, gian cac
tu sach » thu sach, su sach, te sach
sach ky » sac ky, sach y, sach ty
nang xa » nang x, lang xa, nang ma
dan vai » dan va, dan tai, dan vat
vai cua » dai cua, hai cua, lai cua
cua tre » cua te, cuu tre, cua triet
va dan » ca dan, va dao, va dau
bo va » bao va, do va, so va
hien » bien, tien, dien

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

• Performing a fuzzy search may retrieve terms with similar spellings: tu sach ky nang xa hoi. hieu ((vien cac) or (((vien dai) OR (hien dai)))) bo va dan vai cua tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: tu sach ky nang xa hoi. hieu ((vien cac) OR (((vien dai) OR (hien dai)))) bo va dan vai cua tre.
• The words AND, OR and NOT may confuse the search; try adding quotes: "tu sach ky nang xa hoi. hieu ((vien cac) or (((vien dai) OR (hien dai)))) bo va dan vai cua tre".
• Adding a wildcard symbol may retrieve word variants: tu sach ky nang xa hoi. hieu ((vien cac) or (((vien dai) OR (hien dai)))) bo va dan vai cua tre*.