Verbal TC strategy doubt GRE

Hi,

I was going through lecture 3 and came across a question (ss attached below). I would like to understand few things:

1. Why we did not use BY as a support indicator but used comma?

2. What’s the best approach to figure out the support or contrast when multiple indicators are present in question?

Thanks

I guess the best way is to from idea chunking. The logic word (by , comma) should be a seperator between two ideas. So using “By” as a seperator Idea 1 will be: “In an age without radio or recordings, an age ____” by Idea 2: “print”. Now this is an incomplete idea and even after that this doesnt tell anything about print, is it an age ruled by print or an age ignored by print. So using comma as a seperator helps.