1. Security inks exploit the same principle that causes the vivid and constantly changing colours of a film of oil on water. A. When two rays of light meet each other after being reflected from these different surfaces, they have each travelled slightly different distances. B. The key is that the light is bouncing off two surfaces, that of the oil and that of the water layer below it. C. The distance the two rays travel determines which wavelengths, and hence colours, interfere constructively and look bright. D. Because light is an electromagnetic wave, the peaks and troughs of each ray then interfere either constructively, to appear bright, or destructively, to appear dim. 6. Since the distance the rays travel changes with the angle as you look at the surface, different colours look bright from different viewing angles.
2.
1. Commercially reared chicken can be unusually aggressive, and are often kept in darkened sheds to prevent them pecking at each other. A. The birds spent far more of their time?up to a third?pecking at the inanimate objects in the pens, in contrast to birds in other pens which spent a lot of time attacking others. B. In low light conditions, they behave less belligerently, but are more prone to ophthalmic disorders and respiratory problems. C. In an experiment, aggressive head-pecking was all but eliminated among birds in the enriched environment. D. Altering the birds? environment, by adding bales of wood-shavings to their pens, can work wonders. 6. Bales could diminish aggressiveness and reduce injuries; they might even improve productivity, since a happy chicken is a productive chicken.
3.
1. The concept of a ?nation-state? assumes a complete correspondence between the boundaries of the nation and the boundaries of those who live in a specific state. A. Then there are members of national collectivities who live in other countries, making a mockery of the concept. B. There are always people living in particular states who are not considered to be (and often do not consider themselves to be) members of the hegemonic nation. C. Even worse, there are nations which never had a state or which are divided across several states. D. This, of course, has been subject to severe criticism and is virtually everywhere a fiction. 6. However, the fiction has been, and continues to be, at the basis of nationalist ideologies.
4.
1. In the sciences, even questionable examples of research fraud are harshly punished. A. But no such mechanism exists in the humanities?much of what humanities researchers call research does not lead to results that are replicable by other scholars. B. Given the importance of interpretation in historical and literary scholarship, humanities researchers are in a position where they can explain away deliberate and even systematic distortion. C. Mere suspicion is enough for funding to be cut off; publicity guarantees that careers can be effectively ended. D. Forgeries which take the form of pastiches in which the forger intersperses fake and real parts can be defended as mere mistakes or aberrant misreading. 6. Scientists fudging data have no such defences.
5.
1. Horses and communism were, on the whole, a poor match. A. Fine horses bespoke the nobility the party was supposed to despise. B. Communist leaders, when they visited villages, preferred to see cows and pigs. C. Although a working horse was just about tolerable, the communists were right to be wary. D. Peasants from Poland to the Hungarian Pustza preferred their horses to party dogma. 6. ?A farmer?s pride is his horse; his cow may be thin but his horse must be fat,? went a Slovak saying.
