Khi?m th? l� thu?t ng? ???c d�ng ?? ch? b?t c? d?ng b? m?t th? gi�c n�o, d� ?� l� ng??i kh�ng nh�n th?y g� h?t hay l� ng??i ch? b? m?t m?t ph?n th? gi�c. M?t s? ng??i b? m� ho�n to�n.

T�m ki?m t�i li?u d??i ?�y.