Which of the given era, is to keep the theater alive, minstrels, though denounced by the Church, performed in markets, public places, and festivals?

The era you're referring to is the Middle Ages. During this time, minstrels, despite being denounced by the Church, performed in markets, public places, and festivals to keep the theater alive. Here are the steps to arrive at this answer:

1. Identify the key elements in the question: "era", "theater alive", "minstrels", "denounced by the Church", "markets", "public places", "festivals".

2. Research or recall from knowledge the era when minstrels were prominent and the Church had a significant influence. This points to the Middle Ages.

3. Confirm this by noting that during the Middle Ages, minstrels often performed in public places like markets and festivals, and the Church was known to denounce such performances.

4. Therefore, the era referred to in the question is the Middle Ages.