Преобразуйте предложения в past perfect и present perfect. 1.it presents the mechanism for survival. 2.they are able to carry out the task of production. 3.it is possible to group these structures into four broad categories. 4.these methods are based on tradition. 5.a son follows in the footsteps of his father and uses the same skills and tools. 6.the distribution problem is solved in a similar manner. 7.they receive shares according to an ancient custom. 8.tradition plays some part in economical processes.

Past Perfect обозначу как  P1
Present Perfect - P2

1. P1  - It  had presented the mechanism for survival for years.
P2 - It has  just presented the mechanism for survival.
2. P1 - They had been able to carry out the task of production by Monday.
P2- They has just been able to carry out the task of production. 
3. P1 - It had been  possible to group these structures into four broad categories by that time.
P2 - It has just been  possible to group these structures into four broad categories. 
4. P1 - These methods had been based on tradition for a long time.
P2 - These methods has already been based on tradition.
5. P1 - A son had followed  in the footsteps of his father and used the same skills and tools by the time he was  20 years old.
 P2 - A son has already followed  in the footsteps of his father and used the same skills and tools. 
6. P1 - The distribution problem had been solved in a similar manner for a long time.
P2 - The distribution problem has already been solved in a similar manner. 
7. P1 - They had received shares according to an ancient custom for 5 years. 
P2 - They have just received shares according to an ancient custom. 
8. P1 - Tradition had played some part in economical processes. 
P2 - Tradition has already played some part in economical processes.