Which sentence uses correct subject-verb agreement?

A good coach teach focus and persistence.

The athlete trains for several hours every day.

Athletes at all levels can improves with practice.

The student handbook explain the contest rules.

The sentence that uses correct subject-verb agreement is The athlete trains for several hours every day.

This sentence applies the third-person rule adding 's' to the verbs in present that had the singular third-person subject he, she or it. "Train" became "trains".

For the sentence "A good coach teach focus and persistence." the correct form would be "a good coach teaches focus and persistence."

For the sentence "Athletes at all levels can improves with practice." the correct form would be "Athletes at all levels can improve with practice."

For the sentence "The student handbook explain the contest rules." the correct form would be " The student handbook explains the contest rules."

(b) The athlete trains for several hours every day.