The correct answer is 512 bits. If a block length is fewer than 512 bits, padding bits are added to make the block length equal to 512 bits.
The other answers are distracters.

A certification authority (CA) is an entity that issues digital certificates (especially
X.509 certificates) and vouches for the binding between the data items in a certificate. An issuing authority could be considered a correct answer, but not the best answer, since it is too generic.
Source: SHIREY, Robert W., RFC2828: Internet Security Glossary, may 2000.

In biometrics, identification is a "one-to-many" search of an individual's characteristics from a database of stored images.
Source: KRUTZ, Ronald L. & VINES, Russel D., The CISSP Prep Guide: Mastering the
Ten Domains of Computer Security, 2001, John Wiley & Sons, Page 38

The public key would be found. The public key is used to validate the Digital
Signature contained within the Digital Certificate. As you well know the private key would never be distributed and only the owner of the certificate would have a copy of the private key.
In cryptography and computer security, a root certificate is either an unsigned public key certificate or a self-signed certificate that identifies the Root Certificate Authority (CA). A root certificate is part of a public key infrastructure scheme. The most common commercial variety is based on the ITU-T X.509 standard, which normally includes a digital signature from a certificate authority (CA).
Digital certificates are verified using a chain of trust. The trust anchor for the digital certificate is the Root Certificate Authority (CA).
A certificate authority can issue multiple certificates in the form of a tree structure. A root certificate is the top-most certificate of the tree, the private key of which is used to "sign" other certificates. All certificates immediately below the root certificate inherit the trustworthiness of the root certificate - a signature by a root certificate is somewhat analogous to "notarizing" an identity in the physical world. Certificates further down the tree also depend on the trustworthiness of the intermediates (often known as "subordinate certification authorities").
Many software applications assume these root certificates are trustworthy on the user's behalf. For example, a web browser uses them to verify identities within SSL/TLS secure connections. However, this implies that the user trusts their browser's publisher, the certificate authorities it trusts, and any intermediates the certificate authority may have issued a certificate-issuing-certificate, to faithfully verify the identity and intentions of all parties that own the certificates. This (transitive) trust in a root certificate is the usual case and is integral to the X.509 certificate chain model.
The root certificate is usually made trustworthy by some mechanism other than a certificate, such as by secure physical distribution. For example, some of the most well- known root certificates are distributed in the Internet browsers by their manufacturers
The following answers are incorrect:
The Private Key is never distributed, only the owner would have a copy of the private key.
Symmetric keys have no direct relation to Public Key cryptosystems.
A recovery key is usually used with full drive encryption tool when a user has lost or damage his key.
The following reference(s) were/was used to create this question:
http://en.wikipedia.org/wiki/Root_certificate
and
Getting a root CA accepted within browsers