UNIT 8: THE ULTIMATE SURVIVOR - Exercise 1

Read the following passage about friendship and mark the letter A, B, C, or D on your answer sheet to indicate the option that best fits each of the numbered blanks from 18 to 22.
For a nervous horror fan, an evening watching HBO’s hit post-apocalyptic television show The Last of Us ___(1)___. The silhouette of a coat slung over the back of a chair or even the screeching of a cat in the garden will cause a spike of adrenaline. Animals are primed to be wary through natural selection rather than scary television shows, but like humans, they often make mistakes when watching out for threats. Identifying stealthy predators ___(2)___. From the perspective of a songbird, a harmless crow flying overhead may look similar to a raptor. But predator identification is made more challenging by the fact that prey animals often juggle multiple activities like foraging, ___(3)___, and courting mates, all at the same time.
This can be made easier by working as a group. Members of a school of fish, flock of birds or herd of antelope can share the task of watching out for predators. When an animal detects a predator, they share this information with other group members directly, by producing a warning, or inadvertently, by preparing to flee. The group as whole can then respond by fleeing, hiding or adopting a defensive position. But this information is not always reliable. When predators are harder to identify, perhaps because they are well camouflaged, an animal may be more likely to mistake unrelated sounds or movements for a predator. Research found that bumblebees were more likely to produce false alarms having previously been exposed to highly camouflaged goldenrod crab spiders than bees ___(4)___. Some species are instead simply more vulnerable to predators than others. This can be because ___(5)___ or not equipped to fight a predator off. For these species, ignoring a true alarm is more likely to result in death, so it may be beneficial to follow a “better-safe-than-sorry” principle and pay the cost of being occasionally wrong. Willow tits produce alarm calls in response to most large aerial objects including planes and crows. This is because they are typically hunted in ambush attacks in which they are unlikely to escape. So the costs of alarm calling at a few planes becomes dwarfed by the threat of being killed in an attack.
In some circumstances, the cost of fleeing unnecessarily is higher and an animal may require more certainty about the risk posed by a potential threat before taking evasive action. Semipalmated sandpipers can double their body mass during staging which means that flight will require substantially more energy. False alarms were found to be less common later in staging when body mass was higher and escape flights were more costly.
(Adapted from https://theconversation.com/why-prey-animals-often-see-threats-where-there-are-none-and-how-it-costs-them-200864)