Respuesta :
The first sentence in the question has the captions broken at logical places.
The right sentence is:
I live right by the mountains, and so
I only go to the beach with my
friends during the summer.
The comma in this sentence was rightly placed in where it ought to be. Also the sentence is one but it was broken separated into two using comma so that it can be read easily.
Also unlike other sentences in the question, the first word after the comma does not start with a capital letter.
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