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.

Explanation:

the tone of the passage is sympathetic to the forbidden love of romeo and juliet. the nurse plays a significant role in the play. she is responsible for making their meeting again possible. additionally, there is a sense of warning in the choice of words of the nurse. she seems to be authoritative when she calls romeo "scurvy knave", and at the same time the fact that she addresses to him as "sir" reflects respect. the nurse is "vexed", this word describes her confused state of mind. on the one hand, she finds romeo a fine and eloquent man, but on the other, it is thought that man's nature forces men to try to trick women.  

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