Question

[ánh tuyết nguyễn]

• For questions (1 - 8), read the text below and think of the word which best fits each gap. Use only one word in each gap. There is an example at the beginning (0).

                                                                                                      BLUE DIAMONDS

  Blue diamonds are the world’s most expensive diamonds, with some valued (0) ...... AT....... over 350 million US dollars. However, no one knew (1) ............... recently precisely where these rare stones came from.

  Most diamonds are formed from pure carbon under extreme heat 150 to 200 kilometers underground, and (2) ............... is thought that volcanic eruptions bring them to the earth’s surface. Research by scientists has revealed, however, that blue diamonds were probably formed somewhere (3) ............... 600 and 800 kilometers down, in a part of the earth’s interior known (4) ............... the lower mantle.

  These researchers analyzed 46 blue diamonds, all of (5) .............. contained minerals only found in the lower mantle. (6) .............. only were these stones formed four times nearer the earth’s core (7) ............... normal diamonds, but they also contain an element called boron that is mostly found on the earth’s surface. What seems to have happened, (8) ............... to the researchers, is that billions of years ago, rocks containing boron were carried down into the lower mantle by movements of the earth’s tectonic plates, and were eventually returned to the surface by volcanic action.

Answer 1

[_silverlining]

until?

it

between

as

which

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than

according