Explanation/Reference:
A: Public (asymmetric) key encryption uses a pair of keys, one private and one public.
The public key is freely distributed to any party that may wish to send encrypted data. Once encrypted, data can only be decrypted with the private key. Therefore the private key is maintained by the receiving party and is not shared with anyone else.
The two keys are mathematically related, but can't be used to discover each other.
D: A combination of symmetric and asymmetric encryption is often used.
Incorrect answers:
B: Since public key encryption avoids the need to share a common key, it is generally considered to be more secure.
C: The downside with asymmetric key encryption is that it involves far more complex processing compared to symmetric key encryption, which significantly increases the overhead involved with the encryption and decryption process.
E: It is used to encrypt data.
Reference: Oracle Reference Architecture, Security , Release 3.1