题目

Colorado farmer Chris Jessen and his wife Pam became the newest owners of a “panda cow” when it was born on their farm on New Year's Eve.The calf(小牛)，named Ben，was created through genetic engineering.Ben was the second   panda cow born on Jessen's farm，but was a surprise，Jessen said that he was expecting a black calf. This rare breed of panda cow gets its nickname from its similarity to a panda bear.Its white face and black fur around its eyes are extremely panda­like.There is a white belt circle around the middle part of its black body.Baby Ben has a black mark on it已知与成反比例，当时，，则当时，     .