1. It's because Chuchu felt that his old master was near.

2. It's because Chuchu felt that his old master was near to him.

3. It's because Chuchu felt that his old master was close to him.

4. It's because Chuchu felt that his old master was near him.

5. It's because Chuchu felt that his old master was so near him.

6. It's because Chuchu felt that his old master was so near to him.
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Are the sentences all grammatical? At the end of each sentence, there are changes.

1 answer

Sentences 1-4 are fine.

Sentences 5 and 6 need to be completed. The word "so" here indicates that there's a "that..." clause expected.

... was so near that Chuchu could smell him.
(or some way to complete the thought that "so" begins)