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  • Long ago, wells (1) ________ (dig) in the ground using percussion drilling. A heavy wooden cutting tool (2) ________ (suspend) by a rope from a pulley on a wooden tripod. The tool (3) ________ (pull up) by hand or steam engine, and then it (4) ________ (drop) into the hole. The rock (5) ________ (break) by the weight of the tool. The maximum depth was only about 70 metres.

    Nowadays, much deeper oil wells of 700 m (6) ________ (dig) using a method called rotary drilling. A sharp drill bit (7) ________ (suspend) by a drill string from a pulley on a steel derrick. The drill bit (8) ________ (rotate) in the hole by a powerful engine. The rock (9) _______ (break) by the rotation of the drill bit.

    Now there is also a new method of drilling which (10) ________ (cut) the rock using lasers. No cutting tool or drill bit (11) ________ (use). Instead, the rock (12) ________ (split) by beams of high-energy light. A fibre-optic cable (13) ________ (carry) the light from the lasers on the surface down the hole to a set of lenses. The lenses then (14) ________ (focus) the light to a sharp point on the rock face, which (15) ________ (cut) almost 100 times faster than by a drill bit. As a result, the cost of drilling (16) ________ (reduce), and drilling jobs (17) ________ (complete) much more quickly.

  • 1. were dug
    2. was suspended
    3. was pulled up
    4. was dropped
    5. was broken
    6. are dug
    7. is suspended
    8. is rotated
    9. is broken
    10. cuts
    11. is used
    12. is split
    13. carries
    14. focus
    15. is cut
    16. is reduced
    17. are completed