By 1999, astronomers had discovered 17 nearby stars

By 1999, astronomers had discovered 17 nearby stars that are orbited by planets about the size of Jupiter.

1 Explanation

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Adam

We need the past perfect to denote an event that occurred before a specified time in the past, so eliminate (D) and (E). (B) and (C) are unnecessarily wordy. (A) presents the information in the most concise manner.

Sep 1, 2017 • Comment

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Section 9.6 Sentence Correction

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137. By 1999, astronom...
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139. In no other histo...
140. Rock samples take...

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