Hello!
The best way to revise this sentence is: The capital of Japan—I have read that this huge city has over 30 million people—is Tokyo.
Why?
We must know the puntuaction marks in order to choose the best way to revise this sentence. Punctuation marks are used in English grammar to help us to redact sentences to make it understandable to the reader.
Em dash or long dash (—) are used to give an explanation, descriptions or definitions of something in the middle of a phrase.
So, checking the given options and knowing what a long dash is, the best way to revise this sentence is: The capital of Japan—I have read that this huge city has over 30 million people—is Tokyo.
Have a nice day!
