Alessandra has an encryption key pair, where she keeps one key secret and publishes the other. Alessandra wants to send Bruno an important document. She encrypts it using her own secret (private) key before sending it to him. Bruno then decrypts the document using Alessandra's published (public) key.

What purpose does Alessandra achieve by doing this?

A. She can substitute a phony document for the one she promised Bruno.
B. She makes the document available to anyone who wants to see it.
C. She guarantees that the document has no spelling errors.
D. She convinces Bruno that the document came from her.