Explanation
The way that a marketer can avoid emailing prospects more than once in a ten day span is to use a dynamic list to create a frequency suppression list. A dynamic list is a type of list that automatically updates based on specific criteria, such as field values, activities, or scores. A frequency suppression list is a type of list that excludes prospects who have been emailed within a certain time frame, such as ten days. By using a dynamic list with a frequency suppression criteria, a marketer can ensure that they do not email prospects who have already received an email recently. Using an automation rule, a global account setting, or a segmentation rule are not ways that a marketer can avoid emailing prospects more than once in a ten day span, as they either do not create lists, do not update automatically, or do not run continuously2. References: 2: Dynamic Lists

Explanation
You can delete a prospect through the prospect table actions. The prospect table is a list of all the prospects in your Marketing Cloud Account Engagement account, which you can access by navigating to Prospects > Prospect List. From there, you can select one or more prospects and click on the Tools button to see the available actions. One of the actions is Delete, which will permanently remove the selected prospects from your Marketing Cloud Account Engagement account. You can also delete a single prospect by clicking on their name and then clicking on the Delete button on their record.
Answer A is incorrect because you cannot delete a prospect through a completion action. A completion action is a task that is performed after a prospect successfully completes a marketing element, such as a form, landing page, or custom redirect. You can use completion actions to perform various actions on prospects, such as sending emails, adjusting scores, changing campaigns, or adding tags, but not deleting them. Answer B is incorrect because you cannot delete a prospect through an automation rule. An automation rule is a criteria-based action that is triggered when a prospect matches the rule. You can use automation rules to perform various actions on prospects, such as sending emails, adjusting scores, changing campaigns, or adding tags, but not deleting them. Answer C is incorrect because you can delete prospects, as explained above.
References: Prospect List, [Delete Prospects], [Completion Actions], [Automation Rules]

Explanation
If a Marketing Cloud Account Engagement administrator wants to keep the first value submitted in a field even if the prospect completes additional forms with different values for that field, they should enable the form field option "Maintain the initial value upon subsequent form submissions" (A). This option prevents the field from being overwritten by later submissions. The option "Always display even if previously completed" (B) does not affect the field value, but only the field visibility on the form. The option "Kiosk/Data Entry Mode:
Do not cookie browser as submitted prospect" does not affect the field value, but only the prospect tracking method. The option "Include "Not you?" link to allow visitors to reset the form" (D) does not affect the field value, but only the form reset functionality. References: Create a Form