The children are playing.
Abbreviation steps:
Understand the meaning of the sentence;
Mark the words, trunk and branches that must be reserved;
Check the pros and cons of right and wrong. For example: "The children are playing happily in the garden", "happily in the garden" as adverbial, delete. So it is reduced to: children are playing.
When shortening sentences, we should pay attention to three points: first, we should not change the meaning of the original sentence, second, we should not change the structure of the original sentence, and third, we should still abbreviate the sentence.
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