<u>Answer:</u>
Stop [!] the train is approaching.
<u>Explanation:</u>
The punctuation should be an exclamation point because it used at the end of a sentence or a short phrase which expresses very strong feeling.
<em>Hoped this helped.</em>

Answer:
There has been a <em><u>plethora</u></em> of phone calls from worried customers for the past two days.
Explanation:
The perfect word choice :-)
Answer:
Her car would not start, therefore, she was late for class
Explanation:
Hope this helps! If it's a run on you can add a comma and an extra word. Commas separate 2 ideas into one sentence
The animal who is the first to commit the rebellious act is Napoleon. He had Snowball chased from Animal Farm using nine vicious dogs. After Snowball's exile, Napoleon assumed leadership.