Final answer:
A sentence does not always end with a punctuation mark when it ends with a double dash, as the dashes often indicate a break or emphasis within the sentence rather than the end. Therefore, the statement is false.
Step-by-step explanation:
The statement is false. Not every sentence should end with a punctuation mark when it ends with a double dash. In English grammar, double dashes are used to set off or emphasize content within a sentence, and they often function in a similar way to parentheses or commas. However, the sentence usually continues after the double dashes if they are placed mid-sentence. If the double dash is used at the end of a quote within a sentence, punctuation such as a period or comma would typically follow the closing quotation mark.
Let's look at some examples of how dashes can be used:
Example 1 - The U.S.S. Constitution became known as "Old Ironsides" during the War of 1812—during which the cannonballs fired from the British H.M.S. Guerriere merely bounced off the sides of the Constitution.
Example 2 - To some of you, my proposals may seem radical—even revolutionary.
In these examples, the dashes add emphasis and are not necessarily at the end of the sentence. Also, punctuating sentences correctly helps to indicate separation of ideas and can prevent run-on sentences. Thus, if a sentence ends with a double dash, usually there is more to the sentence, or there is an interruption in thought, and a follow-up punctuation mark might be necessary unless the sentence is intentionally left unfinished.