Final answer:
The sentence demonstrating correct comma usage is 'The news media, including newspapers, news magazines, radio and television, are an important source of information in this country.'. The commas correctly separate the list and make the sentence more understandable.
Step-by-step explanation:
The sentence which demonstrates correct comma usage is: a. The news media, including newspapers, news magazines, radio and television, are an important source of information in this country.
Proper use of commas in a sentence helps in separating items in a list or clause. In this sentence, the correct usage involves placing a comma after 'media', before the list of various news mediums, and at the end of the list before continuing with the sentence.
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