What will undelete a prospect?

You can undelete a prospect if the deleted prospect is imported into Marketing Cloud Account

Engagement with the same email address or if the deleted prospect re-converts by filling out a form

with the same email address. When you delete a prospect, they are removed from your Marketing

Cloud Account Engagement account, but their record is not completely erased. You can restore them

by importing them again or by having them fill out a form again, which will update their existing

record and undelete them. However, you cannot undelete a prospect if they visit a web page, as this

will not trigger any action on their record.

Answer B is incorrect because visiting a web page will not undelete a prospect, as explained above.

Reference: Delete Prospects, Undelete Prospects