Final answer:
Option b) Customers are 35% more likely to recommend your store to a friend.
Step-by-step explanation:
The evaluation indicator that would answer the evaluation question, 'Are customers paying attention to our email newsletters?' would be option b) Customers are 35% more likely to recommend your store to a friend.
This indicator suggests that customers are engaged with the store's content and find it valuable enough to recommend to others.
It implies that customers are reading the email newsletters and finding them useful.