The manager of a music store wants to find out what percentage of headphones that were sold are defective. which sampling methods are likely to be biased? select each correct answer. question 6 options: a) the manager selects 20 customers at random each day for 2 days and contacts them. b) every 20th customer over the course of a week is selected and their answer recorded. c) on 1 day, an hour after the store opens, the first 10 customers are surveyed. d) the manager sends an email to 20 customers who purchased headphones from the store, asking each customer if the headphones were defective. the first 5 responses are recorded.