A roll-up summary field is used to display a value in a master record based on the values of a set of related detail records. In this case, the administrator can create a roll-up summary field on the Properties object that counts the number of Open House records in a Pending status. Reference: https://help.salesforce.com/s/articleView?id=sf.fields_about_roll_up_summary_fields.htm&type=5 A permission set is a collection of settings and permissions that give users access to various tools and functions. The View All Data permission allows users to view all data, regardless of sharing settings. By creating a permission set with this permission and assigning it to the subset of users, the administrator can meet the requirement without changing their profiles or roles. Reference: https://help.salesforce.com/s/articleView?id=sf.perm_sets_overview.htm&type=5 https://help.salesforce.com/s/articleView?id=sf.admin_general_permissions.htm&type=5

Duplicate management is a feature that allows administrators to prevent or allow duplicate records for standard or custom objects. Duplicate management consists of two components: duplicate rules and matching rules.
* B) Configure custom duplicate rules.
Duplicate rules are rules that determine what actions to take when users try to save duplicate records.
Duplicate rules can block users from saving duplicates, alert users of duplicates and let them save anyway, or report on duplicates without affecting the save operation. Duplicate rules can also specify which fields to use for matching and which security settings to enforce. By configuring custom duplicate rules, the sales team administrator can prevent duplicate records from being created for contacts or other objects. References:
https://help.salesforce.com/s/articleView?id=sf.data_prevent_duplicates.htm&type=5
* C) Create custom matching rules.
Matching rules are rules that determine how duplicate records are identified by comparing fields and applying fuzzy matching algorithms. Matching rules can be standard or custom. Standard matching rules are predefined by Salesforce and apply to common objects such as contacts, accounts, or leads. Custom matching rules are created by administrators and apply to any standard or custom object. By creating custom matching rules, the sales team administrator can define how duplicate records are detected for contacts or other objects.
References: https://help.salesforce.com/s/articleView?id=sf.data_matching_rules.htm&type=5

Use Field-Level Security to control data access is how the administrator should deliver this solution. Field-Level Security is a way to restrict users' access to view or edit specific fields on an object based on their profile or permission set. Field-Level Security can be used to make fields visible or hidden, and editable or read-only for different users. By using Field-Level Security, the administrator can ensure that only Marketing users can see all data on the Membership Details object, while Support users can only see the Support preference fields.