4 Study the sentences from the quiz. Then choose the correct words in the rules.
1 By the time he returned to Venice in 1295,
Marco Polo had travelled almost 24,000 km.
2 Gagarin had flown in a plane hundreds
of times, but he had never flown in a
spacecraft.
RULES
a We form the past perfect with have /
had and a past participle.
b We form negative sentences with not or
ever / never
c We use the past perfect to talk about
an action that happened before / after
another action in the past.​

1. We have finished all our homework.

 2.He has visited us many times  

 3.She has returned my book at last

 4.I am afraid that I have lost my car keys.

 5. We have been in Mexico many times.

 6. I have studied this exercise before.

 7. We have learned many new words in this course.

 8.My family has been to Montreal.

 9. I have heard that story before.

 10.We have lent money to them several times.

 11.Mr. Petridis has gone to South America to work.

 12. His uncle has taught computer science for years.

 13. She has seen that movie three times.

14. He has make and lost several fortunes.

 15. Kelly has tried that recipe many times.

 16.He has begun to understand what Alice wants .

 17. The flowers have grown very high.

 18. They have been in Acapulco many times.

 19. Dick has visited them in Mexico twice.

Who has not heard many stories about these cetaceans of friendly and cute animals. Science knows more than 50 species of dolphins. The most common delfiny - squirrel and bottlenose dolphins (normal). These animals live in packs. They can be found not only in temperate and warm waters of the oceans, seas and even in rivers and lakes. Dolphins are interesting because they have a highly developed nervous system. In addition, studies have shown that their brains like a man, and the convolutions of the cerebral cortex of a dolphin twice as much as in humans. The bark of the brain consists of 6 layers (as a person), and brain cells a half times more. Dolphins, like some whales emit ultrasounds that are used for communication and oriyentatsiyi.Tsikavo that each dolphin has its own tone of voice. "Turning" to "companion" dolphin mimics the tone of voice of someone to "calls" .In the lexicon of dolphin discovered more than 30 sounds, some of them warn about the dangers others help keep the pack together, but this is only a small fraction decoded sounds.