Read the passage below. Based on the rules of Standard English conventions, which punctuation mark must fill the blank to correctly set off the nonessential element?
Answer:In 1735, the self-taught English clockmaker John Harrison presented his first marine chronometer—a revolutionary timekeeping device designed to accurately calculate longitude at sea【—】to the British Board of Longitude. Harrison’s ingenious invention solved a monumental navigation problem that had baffled scientists for centuries, enabling sailors to safely navigate the open ocean by determining their precise east-west position.
Answer
An em dash (—)
The correct punctuation mark is an em dash because the nonessential appositive phrase 'a revolutionary timekeeping device designed to accurately calculate longitude at sea' is opened with an em dash. Under Standard English conventions, nonessential elements must be set off with matching pairs of punctuation (comma-comma, dash-dash, or parenthesis-parenthesis). Thus, an em dash must be used to close the phrase to maintain punctuation symmetry.
Step-by-Step Solution
Key Concept
Punctuation of Nonessential Elements