Final answer:
Progressive profiling is a technique used in form design to gradually show fields to the user over time. For this scenario, option B: Number of blank fields = 3 is the correct choice.
Step-by-step explanation:
Progressive profiling refers to a technique used in form design where fields are gradually shown to the user over time, rather than all at once. The goal is to collect necessary information from the user without overwhelming them with too many fields.
In this case, you have three mandatory fields that you always want to show on the form, and you want a total of five fields visible to the user. Since you have three mandatory fields, you should choose option B: Number of blank fields = 3. This means that two additional fields will be shown to the user over time, resulting in a total of five fields.