Joe said, "Know what, Charlie? I killed 5 flies yesterday, 3 males and 2 females."

　　"How could you tell  them  apart , Joe?" asked Charlie.

　　Joe replied, "That was easy. The 3 males were sitting on a case of beer and the 2 females were on the phone."

Key words：

tell    apart　分辨、辨識

case　（n.）箱