Fill in can, have to, may, might, must, need, should or (not) allowed to. 1. You ... be tired because you have worked very hard.
2. He ... come to my party because he is ill.
3. He ... go to the dentist when he has toothache.
4. It`s not very important. You ... not do it now. You ... do it tomorrow.
5. ... you speak many languages?
6. I don`t know what I`m doing this weekend, but I ... go to London.
7. Smoking is very unhealthy. You ... stop it.
8. Playing football ... in this park.
9. You have got plenty of time. You ... not hurry.
10. You ... have a passport to visit most foreign countries.

1. Text 5 goes under the title "Phosphorus" and describes this element in the Periodic Table in great details.
2. The author gives many interesting facts concerning the properties and peculiarities of phosphorus and compares it with (w/) nitrogen.
3. Firsly, phosphorus and nitrogen have much in common, but they also differ greatly.
4. While nitrogen is quiete inactive under ordinary conditions, phosphorus reacts rapidly both w/ metals and non-metals.
5. At ordinary temperature, nitrogen is a gas, and phosphorus is a solid.
6. Secondly, phosphorus has the following properties:
- it is almost insoluble in water;
- it dissolves in many solvents.
7. The article goes on that phosphorus exists in several aliotropic forms, only 2 of them are of general interest. One is white phosphorus.
8. The most striking property of white phosphorus is its activity w/ oxygen.
9. It is very combustible, that's why it must be left under water.
10. The author gives some measures of precaution while handling white phosphorus.
11. They are as follows:
- never handle white phosphorus w/ bare hands;
- always remember that it's very poisonous, it may cause chronic poisoning.
12. In the conclusion, it should be mentioned that red phosphorus is a more stable form. It isn't so combustible, but the products formed are the same produced by white phosphorus.
That's about all;-)

Man pollutes the environment with household and industrial waste. It is a by-product of civilization. Hundreds of years ago, factory and furnace pipes threw clouds of black poisonous coal smoke into the air. Now there are even more factories, and with them the substances that poison the air, water and land: they are even in Antarctica and the Himalayas. So far, we can only limit harmful emissions, recycle household waste and waste, and use materials that are decomposed by living organisms, such as soil bacteria.

The ozone layer traps the sun's ultraviolet rays, which cause skin cancer. Against the background of chronic environmental pollution, ecological catastrophes sometimes occur. For example, in the event of an accident, oil spills out of the tanker's hold and forms a huge spot on the ocean surface. Oil covers animals with a deadly stain. Chlorofluorocarbons, which are used in the manufacture of refrigerators and aerosol cans, rise in the upper atmosphere and destroy the ozone layer. Dangerous "ozone holes" have recently been discovered over the Arctic and Antarctic, and their numbers continue to rise. Exhaust gases contain nitrogen oxides, and the combustion of coal in power plants releases sulfur dioxide. Combining in the air with water, these substances are converted into acids, which then fall out with the rain. Acid rain destroys buildings, destroys forests and ponds. New technologies can reduce emissions, but it costs a lot.

Toxic and other hazardous wastes are often buried. In this case, they kill all living things around, spreading water. The North Sea, once rich in fish, is now almost completely poisoned