“Rubber Duck”,________ by Dutch artist Florentijn Hofman，has visited many cities since 2007．

A．being created

B．creating

C．created

D．having created

程z²x²-y²=0所表示的曲面是（）。

A.旋转双曲面

B.双叶双曲面

C.圆锥面

D.单叶双曲面