Question

recognizing paired signal words
although it was not suited to solving his immediate
problem, silver felt the unusual adhesive might have
some commercial value, and so he demonstrated it to
various colleagues, including fry. at the time, no one had
come up with a use for it, and so the formula for the weak
adhesive was filed away - until the monday morning
when fry came to work with the idea of making sticky
bookmarks that could also be removed without damaging
the book.
—the evolution of useful things,
henry petroski
which pair of phrases signals the passage of time?
○ although it was not suited... silver felt...
○ silver felt... and so he demonstrated it...
○ at the time... until the monday morning....
○... until the monday morning... that could also be...

Explanation:

The phrase "At the time" indicates a specific moment in the past, and "until the Monday morning" shows a progression of time from that past moment to a later time (Monday morning). These two phrases together signal the passage of time. The other options either show a contrast (Although...Silver felt...), a cause - effect relationship (Silver felt...and so he demonstrated...), or do not clearly show a time - passage sequence (..., until the Monday morning...that could also be).

Answer:

At the time... until the Monday morning...