Question

insert two dashes where needed.
place de la concorde a large public square along the seine river in paris marks
the spot of the guillotine that beheaded marie antoinette and louis xvi in 1793.

Explanation:

Step1: Identify the appositive phrase

The phrase "a large public square along the Seine River in Paris" is an appositive that provides more information about "Place de la Concorde". To set off an appositive, we use dashes (or commas, but here we need two dashes).

Step2: Insert the dashes

We insert two dashes around the appositive phrase. So the sentence becomes: "Place de la Concorde -- a large public square along the Seine River in Paris -- marks the spot of the guillotine that beheaded Marie Antoinette and Louis XVI in 1793."

Answer:

Place de la Concorde -- a large public square along the Seine River in Paris -- marks the spot of the guillotine that beheaded Marie Antoinette and Louis XVI in 1793.