B. The field is universally required to save a record on that object.

C. The field is added to every page layout on that object.

These considerations ensure that the field must have a value whenever a record is saved and that it appears on all page layouts for the object

I have some doubts. I agree with both of you guys but for other hand I found this in documentation:

"Web-to-Lead and Web-to-Case request data is not validated by Salesforce. Invalid data isn’t saved when requests are submitted. For example, if your custom field is a currency field and a user enters alphabetic characters such as “Abc” instead of numbers, the request is still submitted but with no value saved in the custom currency field."

(https://help.salesforce.com/s/articleView?id=sf.fields_universally_required_field_considerations.htm&type=5)

So maybe D is also correct.

correct
B. The field is universally required to save a record on that object.
C. The field is added to every page layout on that object.

Correct:
B. The field is universally required to save a record on that object.
C. The field is added to every page layout on that object.