Final answer:
The line of poetry 'Hark! the herald angels sing,' fits a 3/4 time signature due to its natural emphasis and trochaic meter pattern.
Step-by-step explanation:
The line of poetry "Hark! the herald angels sing," perfectly fits into a 3/4 time signature. This time signature, also known as "waltz time", allows for the stress to fall on the first beat of each measure, which aligns with the natural emphasis of the words in the line when sung or recited. The 3/4 time signature supports the trochaic meter, which is characterized by a stressed syllable followed by an unstressed syllable, much like the pattern found in this line of poetry.