题目

 — Hello! Can I speak to Alice? — Sorry. She isn't here. She              to the shop.    A. goes                                   B. has been                      C. has gone 答案：C大多数生物群落在空间上有垂直分层现象，称为群落的垂直结构。引起森林群落中植 物和动物垂直分层现象的主要原因分别是 A．温度、食物          B．温度、光照      C．温度、温度            D．光照、食物