Please explain this line in simpler words.
So serious do this senior citizens become that you would never guess they were novice heated discussion debates on politics and religion have also engrossed a quiet few

Dear Student,

The line 'So serious do these senior citizens become that you would never guess they were novices. Heated discussions, debates on politics, and religion have also engrossed quite a few.' talks about senior citizens, their interests and how they spend time. It tells us about the kind of activities seniors indulge in. Sometimes they get involved in an activity so passionately that no one can make out that they don't know anything about it. They also discuss politics and religion.

Regards