Mutualism is a type of symbiosis that occurs when two unlike organisms live together in a state that is mutually beneficial. It can exist between two animals, between two plants, or between a plant and an animal. Mutualism is unlike the symbiotic state of commensalism in that commensalism is a one-sided state in which a host gives and a guest takes, while in mutualism both partners live on a give-and-take basis.
In the African wilds, the zebra and the ostrich enjoy a symbiotic relationship that enhances the ability of these large land animals to survive. Both serve as prey for the lion, and neither has the capability alone to withstand an attack from this fierce hunter. However, when the zebra and the ostrich collaborate in their defense by alerting each other to possible danger from an approaching predator, the lion is rarely able to capture more than the oldest or feeblest of the herd. The complementary physical strengths and weaknesses of the ostrich and the zebra allow them to work in coordination to avoid succumbing to the lion. The ostrich, the largest flightless bird in the world, possesses great speed and keen eyesight, which enable it to spot large predatory animals long before they are able to position themselves to attack. The zebra, with a running speed equal to that of the ostrich, has excellent hearing and a good sense of smell but lacks the sharp eyesight of the ostrich. When ostriches and zebra intermix for grazing, each animal benefits from the ability of the other to detect approaching danger. If either animal senses danger, both animals are alerted and take off. With the running speed that both of these animals possess, they are able to outrun any predator except the cheetah.
1.Choose the drawing that describes a commensalist state.
2.The difference between mutualism and commensalism is that（ ）.
3.In paragraph 2, the word "that" refers to（ ）.
4.Which of the following drawing describes what happens when a lion approaches a zebra and an ostrich?
5.From the passage, we can learn that（ ）.
问题2选项
A.commensalism is a two-sided state.
B.the partners live on a give-and-take basis in mutualism.
C.the host gives while the guest takes in mutualism.
D.mutualism occurs between two similar organisms; however, commensalism, two unlike organisms.
问题3选项
A.running speed
B.strength
C.weakness
D.eyesight
问题5选项
A.the zebra often offers more help than the ostrich to detect the attack of the lion
B.the zebra and the ostrich are complementary in their abilities of avoiding being attacked by
C.both the zebra and the ostrich possess great speed and keen eyesight
D.with great speed, the zebra and the ostrich run faster than any predator
第1题:B
第2题:B
第3题:A
第4题:D
第5题:B
第1题:
细节事实题。根据原文第一段“Mutualism is unlike the symbiotic state of commensalism in that commensalism is a one-sided state in which a host gives and a guest takes…”可知，互利共生与偏利共生的共生状态并不相同，因为偏利共生是一种单向状态，即宿主给予，寄生物索取。由此可知B项“宿主→寄生物”表述正确，故本题正确答案为B项。
第2题:
细节事实题。题干询问哪一项符合互利共生和偏利共生的区别。根据原文第一段“Mutualism is a type of symbiosis that occurs when two unlike organisms live together in a state that is mutually beneficial. ”可知，互利共生是一种共生关系，当两个不同的有机体生活在一种互惠的状态时就会发生。根据后文叙述的“Mutualism is unlike the symbiotic state of commensalism in that commensalism is a one-sided state in which a host gives and a guest takes...”可知，互利共生与偏利共生的共生状态是不同的，偏利共生是一种单向的状态，即宿主给予而寄生物索取。由此可知A项“偏利共生是一种双向状态”表述错误；B项“靠彼此相互给予和索取合伙共生”表述正确；C项“在互利共生中，宿主给予而寄生物索取”表述错误；D项“互利共生发生在两种类似的生物之间，而偏利共生却发生于两种不同的生物之间”与原文不符。因此，本题正确答案为B项。
第3题:
推理判断题。根据原文第二段“The zebra, with a running speed equal to that of the ostrich, has excellent hearing and a good sense of smell but lacks the sharp eyesight of the ostrich.”可知，斑马的奔跑速度与鸵鸟相当，听觉和嗅觉都很好，但缺乏鸵鸟敏锐的视力。由此可知这里的that指代“running speed（奔跑速度）”，故A项正确。B项strength表示“力量”；C项weakness表示“弱点”；D项eyesight表示“视力”。
第4题:
理判断题。根据原文第二段“If either animal senses danger, both animals are alerted and take off. With the running speed that both of these animals possess, they are able to outrun any predator except the cheetah.”可知，如果两者（即斑马和鸵鸟）中任一种动物觉察到危险，那么两种动物都会警觉起来并迅速奔跑。凭借这两种动物的奔跑速度，它们能够超越猎豹以外的任何捕食者。因此，本题正确答案为D项。
第5题:
推理判断题。根据原文第二段可知，斑马和鸵鸟属于互利共生的关系，它们都是狮子的猎物，都没有能力独自抵抗狮子的攻击，所以它们要进行协同防御，提醒对方可能有危险。如果两者中任一种动物觉察到危险，那么这两种动物都会警觉起来并迅速奔跑。凭借这两种动物的奔跑速度，它们能够超越猎豹以外的任何捕食者。由此可以判断，B项“斑马和鸵鸟在躲避攻击的能力上是互补的”表述正确。而A项“在发现狮子的攻击时，斑马往往比鸵鸟提供更多的帮助”；C项“斑马和鸵鸟都有极快的速度和敏锐的视力”以及D项“由于有非常快的速度，斑马和鸵鸟跑得比任何食肉动物都快”均与原文不符，可排除。
