Multiple choice

Choose the option that best fits gap 23.

Directions: Fill in the gaps with the most appropriate option.

Ever since  Galileo pointed his homemade optical telescope towards the heavens, astronomers---18--------------------building instruments of increasing power and sophistication ---------19--------------------to observe the universe. Hale telescope on Mount Palamar in Southern California can   detect objects a million times smaller than Galileo’s device -----21--------, they still have their limitations. With the advent of radar technology during World War 2, however, astronomy took a great leap outward. With radio antennas pointing to the night sky, astronomers far -----23-------------------their reach.

  1. extends

  2. extended

  3. extending

  4. extension of

Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

We need a form of the word extend in the past tense. The other options are in the present or continuous tense, or they otherwise replace the verb with the noun.

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