A practice of TPO49 (TOFEL), any help will be appreciated :) ! ** question link: http://toefl.kmf.com/question/eb6d8867a1f173c061720b9235adab02/0d9j2k.html The passage and the lecture are both discussing how humpback whales navigate during their long-distanced migration. The author of the passage believes that humpback whales are able to navigate by stars. However, the lecturer holds an opposite opinion. He thinks that the more accepted theory is that they probably navigate by the earth's magnetic fields, and refutes each of the reason mentioned in the passage. First of all, the author points out that humpback whales have complex brain structure, indicating the intelligence able to use star-navigation system. The lecturer challenges the point by saying that there are no absolute relations between the overall intelligence and the ability to navigate by stars. For example, some birds that are able to navigate by stars aren't considered very smart. Secondly, the passage states that animals that can migrate in straights line, including humpback whales, must depend on external signs-- such as the stars-- to orient themselves. The lecturer rebuts this argument and suggests that they probably rely on the earth's magnetic field as the external force instead. Based on the lecture, there is a structure called biomagnetide is found in humpback whales' brain, which may serve as a compass for orientation. Finally, the passage claims that the humpback whales have an unusual behavior called "spy-hopping". They float at the surface and look upward for minutes, as if they are looking at the stars. The lecturer, on the other hand, posits that this behavior has nothing to do with it. Spy-hopping is rare but not unique. He puts forward the idea by mentioning sharks, which do not migrate, also perform spy-hopping to look for their prey, not to look at the stars.