Perhaps you should try some spelling variations:
hanh vai » hanh va, hanh tai, hanh van
hieu va » lieu va, hieu qua
cua tre » cua te, cuu tre, cua triet
nang ma » tang ma, sang ma, nang cao
sach tu » sach thu, cach tu, sach ty
va cam » va cham, va cac, va cao
cam o » cham o, cam lo, ca o
o van » vo van, so van, do van

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 y) or (sach tu)) nang ma hoa. hieu va cam o van ((hanh vai) OR (hanh vi)) cua tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: te ((sach y) OR (sach tu)) nang ma hoa. hieu va cam o van ((hanh vai) OR (hanh vi)) cua tre.
• The words AND, OR and NOT may confuse the search; try adding quotes: "te ((sach y) or (sach tu)) nang ma hoa. hieu va cam o van ((hanh vai) OR (hanh vi)) cua tre".
• Adding a wildcard symbol may retrieve word variants: te ((sach y) or (sach tu)) nang ma hoa. hieu va cam o van ((hanh vai) OR (hanh vi)) cua tre*.