Which sentence is written correctly?
a. maggie broke her leg, while jumping into the pool, and has to wear a cast for eight weeks.
b. snow cones, a tasty treat, can be found in many delicious flavors.
c. the musicians, performed their hit songs, at the weekend concert.
d. mike, has lost 40 pounds, because he started eating healthy and running each day.

B. Snow cones, a tasty treat, can be found in many delicious flavors.

The answer to your question would be that the sentence that is written correctly is the following one: Snow cones, a tasty treat, can be found in many delicious flavors. That is, the correct option would be B.

There should not be a comma before "while" when it means "during the same time". That is why A is incorrect. Then, C and D separate the subject from the predicate with a comma. A comma should not separate a subject from its verb. Writers are tempted to insert a comma there because speakers usually pause at that point in the sentence, but in writing the comma makes the sentence seem stilted.  On the contrary, the information offset with commas in B is an apposition which adds nonessential information to the sentence. That is why it is written correctly.

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