函数零点的个数为

阅读陆游的《卜算子 咏梅》，回答问题。

驿外断桥边，寂寞开无主。

已是黄昏独自愁，更著风和雨。

无意苦争春，一任群芳妒。

零落成泥碾作尘，只有香如故。

      Mr Jones was a millionaire(百万富翁). One day he went to stay at a hotel in New York. He hoped to have the cheapest room to live in. Mr Jones asked, "What price(价格) is the room?". The boss (老板) told him. "And which floor is it on?" Again the boss told him. "Is that the cheapest room you have? I' m staying here by myself and only need a small room. "
     The boss said, "That room is the smallest and cheapest we have. But why do you choose a poor room like that? When your son stays here, he always stays at our dearest room. Yours is the cheapest. " "Yes," said Mr Jones, "his father is a very rich man, but mine isn' t.

日常生活中，用到直流电动机和交流电动机的实例有：（各举几例）

直流电动机： ____；

交流电动机： ____．

下列关于群落的叙述，不正确的是（　　）