题目

假若某生态系统中只有甲、乙、丙三种生物，它们的捕食关系如下图，那么该生态系统中的消费者是（    ） A.甲        B.乙         C.丙       D.乙和丙 答案：D Many people like to keep dogs as their pets．But do you know dogs were not home animals long long ago? The first wild dogs were trained by ___1___ in Europe about 10，000 years ago．These first “dogs” were not like what we have now．They may have been small wolves（狼）．These dogs often came near people to ___2___ some food．Some of the young dogs were kept by people and grew up with them． People believed the dogs were a ___3___ to them in many ways．The dogs helped them to hunt（狩猎）．They could smell and hear danger before people could．They helped keep people warm on cold nights．So it was ___4___ to keep the dogs． Since those early days，people and dogs have always been together．We should not ___5___ them because they are our friends． 1．A．wolves                  B．cats                     C．people                    D．students 2．A．look for                 B．look up                C．look out                 D．look after 3．A．trouble                  B．help                     C．danger                   D．problem 4．A．hard                      B．useless                 C．easy                             D．helpful 5．A．save                      B．like                      C．hurt                       D．feed