Final answer:
The question pertains to which advertising agency was the largest in gross billings in 1917 and the one listed as second, requiring specific historical business records which are not provided here.
Step-by-step explanation:
The question asks about the history of advertising agencies, specifically which agency was listed as the largest in gross billings in the first roster of advertising agencies in 1917, and which one was listed as second. This information is a historical fact related to the advertising industry and its development early in the 20th century.
Without access to historical records or databases which include this roster from 1917, we cannot provide an accurate answer here. Historical data about business rankings and billings such as this are typically sourced from industry reports, historical texts, or archival materials. Hence, it is important to consult reliable historical sources for such specific information.