Perhaps you should try some spelling variations:
hoc sach » hoc sinh, hoc cac, hoc anh
thuc day » thuc dan, thuc vat
cau tren » cu tren, dau tren, ca tren
lang van » dang van, tang van, hoang van
hieu va » lieu va, hieu qua
thuc va » thuc vat, thuc dan
lang xa » lang ha, dang xay
dan vai » dan va, dan tai, dan vat
vai cau » va cau, van cau, vai cac
va nam » van nam, ha 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: hoc sach y ((lang xa) or (lang van)) hoi. hieu va nam ((thuc va) OR (thuc day)) dan vai cau tren~.
• If you are trying to use Boolean operators, they must be ALL CAPS: hoc sach y ((lang xa) OR (lang van)) hoi. hieu va nam ((thuc va) OR (thuc day)) dan vai cau tren.
• The words AND, OR and NOT may confuse the search; try adding quotes: "hoc sach y ((lang xa) or (lang van)) hoi. hieu va nam ((thuc va) OR (thuc day)) dan vai cau tren".
• Adding a wildcard symbol may retrieve word variants: hoc sach y ((lang xa) or (lang van)) hoi. hieu va nam ((thuc va) OR (thuc day)) dan vai cau tren*.