'Front' can be a noun or adjective. 'Middle' is only a noun (in this usage). Therefore, you need 'the' in the front of 'middle' but not necessarily in front of 'front'.
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AnonymousThank you so much as usual and do you feel any difference in meaning between them?No, but I would amend one:
AnonymousI think the #1 is natural and correct. What do you think?I think b
Anonymous so do you mean 'in the front of the sentence' is fine to use for the same meaning, but 'at the front of the sentence' is better to use?Yes.
Anonymous(I would amend one...'Would' is conditional: I would amend one if I were composing the sentence.