Определите время present perfect present perfect progressive past simple рядом с предложением подпишите какое время

1) Density is measured in kilograms per cubic meter.

2) Most materials have a higher density than water and sink in water.

3) The density of the material is very important, especially in aviation.

4) Young's modulus is the ratio of the applied force to the elastic deformation of a given material.

5) The more rigid the metal, the less it deforms under load.

6) when the metal is stretched, it first flows, that is, it is plastically deformed.

7) Lead, copper, aluminum and gold are the most malleable metals.

8) Creep resistance is a very important property of materials used in aircraft engines.

Объяснение:

1. In the past many firms operated (operate) on a cash basis.
2. Our firm  has already extended  (extend) its resources through the use of credit.
3. The automobile agency has not constructed  (construct) its buildings yet. 
4. The company has payed  (pay) mortgage recently.
5. The firm  tripled (triple) the revenue last year.
6. The use of credit (increase)increased  our income last month.
7. We have not produced (produce, not) services for sale since 1980.
8. At last our company has decided (decide) to reduce cash outgo today.