Researchers began their research work with the ancient ears most probably because ______.

A．Anyone can eat ice-cream or other delicious food while walking in his own house.
B．Eating at a counter, one can stand as he likes.
C．An ice-cream is only allowed to be eaten in the streets.
D．The Japanese eating custom does seem to make much sense for many non-Japanese.

A．Use mobile phone in trains unless it is clearly allowed to do so.
B．Leave people some minutes when people are speaking or thinking about an answer.
C．Enter shops, cafes or department stores with a dripping wet plastic umbrella.
D．When indicating an object or direction to someone, wave fingers with the palm downwards.