题目

I was in a strange city I didn’t know at all， and what’s more， I could not speak a word of the language. On my second day I got on the first bus that passed， rode on it for several stops， then got off and walked on. The first two hours passed pleasantly enough， then I decided to turn back to my hotel for lunch. After walking about for some time， I decided I had better ask the way. The trouble was that the only word I knew of the language was the name of the street in which I lived， and even that I pronounced badly. I stopped to ask a newspaper-seller. He handed me a 某水池有浮游动物和藻类两个种群，其种群密度随时间变化的趋势如下图所示。若向水池中投放大量专食浮游动物的某种鱼（丙），一段时间后。该水池甲、乙、丙三个种群中仅剩一个种群。下列关于该水池中上述三个种群间的关系及变化的叙述，正确的是（ ）A．甲和丙既有竞争关系又有捕食关系，最终仅剩下甲种群B．甲和乙既有竞争关系又有捕食关系，最终仅剩下丙种群C．丙和乙既有竞争关系又有捕食关系，最终仅剩下甲种群D．丙和乙既有竞争关系又有捕食关系，最终仅剩下丙种群