Hello. Please let me know if the following sentence is free of errors! Thanks
The topic was so broad and gave me the chance to deepen my understanding of Real Analysis, Functional and Harmonic Analysis, C*-Algebras, Amenability Theory, and Manifold Geometry; the subjects which basically form my research interests.

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Original: The topic was so broad and gave me the chance to deepen my understanding of Real Analysis, Functional and Harmonic Analysis, C*-Algebras, Amenability Theory, and Manifold Geometry; I can say these subjects form my research interests, now.

Suggestion: The topic was very broad and gave me a better understanding of Real Analysis, Functional and Harmonic Analysis, C*-Algebra, Amenability Theory, and Manifold Geometry. These subjects are now my research interests.

It may be good to review the differences between "so", "very", and "too". Hope this helps!
-geoff

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your second draft in the comments section looks much better.

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The topic was so broad and gave me the chance to deepen my understanding of Real Analysis, Functional and Harmonic Analysis, C*-Algebras, Amenability Theory, and Manifold Geometry; I can say these subjects form my research interests, now.

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Please, mention the errors and if it is possible, correct me.

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No real errors, but slightly awkward in two places.