Our body has a powerful army that 1. ………….. it from various types of threats. This personal army is called the immune system. Every day we encounter a huge number of bacteria, viruses and other disease-causing 2. ………..…... However, we don’t 3. ……………… every other day. Which is due to our immune system. The immune system can be broadly divided into two parts – innate and adaptive immunity. Innate immunity is the body’s first natural defense to any intruder. Its main goal is to 4. …………… any intruder from entering the body.
There is also the adaptive immunity. This system is more 5. ……………………….., as it can differentiate between different types of pathogens.
The job of the immune system is to fight these pathogens and get them out of the body. What’s so incredible about the immune system is that it 6. …………………………how to fight the infection, so if the pathogen comes back for round two, the body can beat it off straight away!

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Не спец в английском. Но по-моему, должно быть так
1)
1. My son  can swim
2. We  must meet at 7 o'clock.
3. You must not miss your classes.
4. He has done his homework Now he may go for a walk.
5. You must help your little sister. 

2) используйте Present Simple или Present Progressive. 
1. Tom is in his room. He is playing the piano. (to play)
2. As a rule I go to school by bus. (to go)
3 His sister studies at school. (to study )
4. They are playing football now. (to play)
5. Run downstairs. Your sister is waiting for you (to wait) 

3) употребите past simple в след. предложениях
1. We translated this text last lesson. (to translate)
2. My father went to Moscow yesterday (to go)
3. My friend wrote to me very often last year. (to write)
4. When did you last  go to the theatre? (to go)
5. I didn't see him for three years. (not see)

4) раскройте скобки, употребляя глагол в Past Simple или Past Progressive
1. We were having dinner when you phoned me.
2. Where did  you spend last weekend?
3. My mother was cooking dinner when the lights went out.
4. Last year I went to London.
5. l didn't do my homework yesterday. 

5)раскройте скобки, употребляя глаголы в present,past или future simple Passive. 
1. Books by A. Christie always are read with interest.
2. They often are invited to parties.
3. We were shown a new film last week
4. Tickets will be brought tomorrow.
5. We were given soup for dinner yesterday.

4
1. Is concrete a natural or artificial stone?
2. What kind of properties it has?
3. In what way can concrete be used in moulds?
4. Does it resist fire?
5. Is concrete used in skeleton structures?
6. How many functions have aggregates?
5.
1. In other words aggregates CAN be defined as a mass of practically inert mineral materials, which ...
2. All aggregates both natural and artificial which have sufficient strength and resistance to watering and which do not contain harmful impurities MAY be used for making concrete.
3. As aggregates such materials as sand, pebbles, broken stone, broken brick, gravel,slag, sinder, pumice and others CAN be used.
4. It sets under water, CAN be poured into moulds so as to get any desirable form.
6.
1. can
2. may
3. must
4. can
5. has to help
7.
sets,can be poured, has, resists.- Present Simple.