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Hi. My dissertation is about the evaluation of textbooks based on speech acts and language functions.Would you guide me and give some tips in this case,please?

I think I find your question very broad and unclear in some parts.

For example I am not sure what “speech acts” means, and “language functions” is a vague term too.
And are the “textbooks” language related textbooks? And what kind (i,e. what language topic)?

I feel you should be more specific in what you’re asking to get meaningful answers.