Dear Ms.Sue, thank you for your answer. Will you please help me with one more question?

Do you think it's possible to use such phrases as "for a long time / for a month" in the mid-position, for example: "They have been trying for a week to find a solution to the problem" or does it always go at the end?
Thank you so much.

You're very welcome, Ilma.

Those phrases can usually go either in the middle or at the end. Sometimes they are at the beginning. Adverbs and adverb phrases can usually be placed any where in a sentence, although they are sometimes better close to the verb they modify.

Yes, it is possible to use phrases like "for a long time" or "for a month" in the mid-position of a sentence. While these phrases are commonly placed at the end of a sentence, they can also be placed in other positions depending on the intended emphasis or structure of the sentence.

For example:
- "They have been trying for a week to find a solution to the problem." (mid-position)
- "For a week, they have been trying to find a solution to the problem." (beginning position)
- "They have been trying to find a solution to the problem for a week." (end position)

Ultimately, the placement of these phrases depends on the desired emphasis or flow of the sentence.