Question

which writing mistake is demonstrated in the sentence I have trouble concentrating sometimes. Especially when I can hear people talking.

Answer 1

the answer is actually adverbial clause fragment

Step-by-step explanation:

Answer 2

The second sentence is a sentence fragment. The two clauses should not be broken into two sentences. The second sentence consists only of a dependent clause, so it cannot stand alone as a sentence.

The correct way to write the sentence would be:
I have trouble concentrating sometimes, especially when I can hear people talking.