Question

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:

Las frases "At the time" (en ese momento) y "until the Monday morning" (hasta la mañana del lunes) indican un lapso de tiempo entre dos momentos diferentes. La primera frase establece un punto temporal inicial y la segunda un punto temporal final, lo que sugiere el paso del tiempo.

Answer:

At the time... until the Monday morning.