Question

The poor plague ridden residential areas of the town were shut off from the rest of the world.

Answer 1

Answer: B.

 The poor, plague-ridden, residential areas of the town were shut off from the rest of the world.

The words poor, plague-ridden and residential are adjectives, and it is correct to separate them with commas. -ridden (means full of something unpleasant or bad) is a suffix used to form adjectives; in this case, with  the noun plague it forms the adjective plague-ridden. Shut off  is phrasal verb and doesn't need hyphen.

Answer 2

I think the correct answer would be:
B: The poor, plague-ridden, residential areas of the town were shut off from the rest of the world.