胎儿将生命活动产生的废物排出体外的途径是(  )

   John lives on a farm. The farm is not very big. His parents grow rice and corn. They don’t use animals to do farm work any more. Today they use a tractor(拖拉机). It works faster and better. After he does his work in the fields, he likes to sit and look at the blue sky and the green hills. He thinks the country is more beautiful than the city. In the city, he can’t hear the animals. In the country, he can hear birds singing. He likes to play with his dog, Cody. Cody is a very interesting dog. He likes to follow people. When they stop, he stops.
   When they walk, he walks. John thinks Cody is the best dog of all.

某地一大宅院的灰墙上一幅墨字对联依稀可辩： “放开肚皮吃饱饭，鼓足干劲搞生产”，横批是“多快好省”。这幅对联最早应该书写于（   ）