Identify the word that has been used incorrectly with respect to its approved specific part-of-speech (POS) category. Answer directly with the identified word and do not justify or explain your answer.

Sentence: Check the condition of the back of the machine.
Approved POS: ADV
Answer: back

Sentence: Confirm the close alignment of the parts before assembly.
Approved POS: VERB
Answer: close

Sentence: Maintain a constant keep on the tension of the cable.
Approved POS: VERB
Answer: keep

Sentence: {{sentence}}
Approved POS: {{approved_word_pos}}
Answer: