题目

   A long time ago there were no donkeys in Gui Zhou. One day a merchant from another part of the country went there and took a donkey(驴)with him. Later the donkey got sick and the merchant left it behind and went on his journey. When the donkey was well again, it ran away into the nearby forest.    The tigers in the forest thought that the donkey was a strange animal and they were afraid of it. Whenever it brayed they all ran away as fast as they could.    After a few months, the tigers became friendly with the donkey. They played many games with it, but they still afraid of 花粉植株能否诱导成功与材料的选择密切相关，选择的材料应符合下列哪个条件A．完全开放的花 B．单核居中期花粉C．初花期花粉 D．完全未开放的花蕾