The scenario presents two distinct security concerns: protecting application forms from bot spam and ensuring the privacy of constituent data. A comprehensive solution must address both.

Implementing CAPTCHA (D) is the standard and most direct method to prevent automated bots from submitting spam through public-facing forms on an Experience Site. This directly mitigates the risk of spamming.

Setting the external organization-wide default (OWD) for grant application objects to Private (E) is a foundational security measure. It ensures that a constituent's data is not visible to any other external user by default, which is critical for complying with privacy regulations and securing sensitive information submitted through the forms.

A. "Salesforce Spam Check" is not a specific, standard feature. The correct implementation for bot and spam protection on Experience Sites is CAPTCHA.

B. Requiring a login adds a barrier to entry for new applicants and is a business decision, not a direct technical solution for spam on a public form. CAPTCHA protects public forms without requiring a login.

C. This feature addresses checking application status after submission; it does not provide any security or protection for the initial application form itself.

1. CAPTCHA for Spam Protection (Supports D):

Salesforce Help, Add Google reCAPTCHA to Your Site. This document outlines the procedure for implementing Google reCAPTCHA on Experience Cloud sites, stating, "To protect your site against spam and abuse from 'bots,' you can add a Google reCAPTCHA widget to your login, sign-up, and forgot password pages." This principle extends to any public-facing form, such as a grant application.

2. External OWD for Data Privacy (Supports E):

Salesforce Help, External Organization-Wide Defaults. This documentation explains, "External organization-wide defaults provide separate organization-wide defaults for internal and external users... Setting the default access for external users to Private for an object ensures that a user can see only their own records." This is the primary mechanism for ensuring constituent data privacy in an Experience Site.

3. Public Sector Solutions Security Model (Supports E):

Salesforce Help, Set Up Security for Grants Management. This guide details the necessary security configurations, including, "Configure organization-wide default settings for internal and external access... For external users, set the default access to Private for Funding Award, Funding Award Requirement, Funding Request, and other objects." This explicitly recommends setting the OWD to Private for the core Grants Management objects.