Which of the following is an unstructured question? a. "how many brands of shampoo have you purchased in the past year: 0, 1, 2, 3, 4, 5, or more than 5? " b. "what are the most important characteristics for choosing a brand of shampoo? " c. "were you happy with the quality of the shampoo you purchased (yes/no)? " d. "how satisfied were you with your last shampoo purchase: very unsatisfied, unsatisfied, neutral, satisfied, or very satisfied? " e. "on a scale from 1 to 5 (with 1 being very unimportant and 5 being very important), how important is fragrance when choosing a shampoo? "