Perhaps you should try some spelling variations:
nhanh thai » nhanh thi, nhanh thanh, nhanh thang
khanh thai » khanh thanh, khanh thuan, thanh hai
cau tren » cu tren, dau tren, ca tren
cac luc » cau luc, coc luc, cac nuoc
luc van » luoc van, luu van, duc van
tu sach » thu sach, su sach, te sach
hieu ve » hieu va, hieu van
y nang » ky nang, ly nang, v nang
ve cac » va cac, vien cac
o hai » co hai, so hai, o lai
o hoa » do hoa, so hoa, o ha

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 y nang ((o hoa) or (o hai)). hieu ve cac luc van ((khanh thai) OR (nhanh thai)) cau tren~.
• If you are trying to use Boolean operators, they must be ALL CAPS: tu sach y nang ((o hoa) OR (o hai)). hieu ve cac luc van ((khanh thai) OR (nhanh thai)) cau tren.
• The words AND, OR and NOT may confuse the search; try adding quotes: "tu sach y nang ((o hoa) or (o hai)). hieu ve cac luc van ((khanh thai) OR (nhanh thai)) cau tren".
• Adding a wildcard symbol may retrieve word variants: tu sach y nang ((o hoa) or (o hai)). hieu ve cac luc van ((khanh thai) OR (nhanh thai)) cau tren*.