While cataloging clay fragments excavated beside an ancient irrigation canal in Peru, archaeologist Marisol Vega noticed faint incisions beneath their mineral crusts. The fragments—once classified as undecorated debris but now known, after multispectral imaging, to bear diagrams of branching ______ provide evidence that local planners recorded changes in the canal network.
Which choice completes the text so that it conforms to the conventions of Standard English?
For a sentence with a long interruption, first remove the interrupting material and locate the main subject and verb. Then examine how the interruption begins. If it opens with an em dash and the main sentence resumes afterward, the interruption generally needs a matching em dash at its other boundary.
Hints
Find the main clause
Temporarily remove the words between “fragments” and “provide.” Identify the subject and its main verb.
Track the opening boundary
Notice the punctuation immediately following “fragments” and determine what kind of interruption it begins.
Check the pair
Consider which choice properly marks the point where the supplementary description ends and the main clause resumes.
Step-by-step Explanation
Identify the core sentence
Temporarily remove the long description to reveal the sentence's core structure: “The fragments provide evidence.” “The fragments” is the subject, and “provide” is its verb.
Examine the interruption
The material between “fragments” and “provide” is a supplementary description of the fragments. An em dash after “fragments” marks the beginning of this interruption.
Close the supplementary description
Because the sentence returns to its main structure at “provide,” a second em dash must close the interruption after “waterways.” Therefore, “waterways—” is correct.