Which option can be used to authenticate the IPsec peers during IKE Phase 1?

A.
Diffie-Hellman Nonce

B.
pre-shared key

C.
XAUTH

D.
integrity check value

E.
ACS

F.
AH

Explanation:
http://www.cisco.com/en/US/docs/ios/12_2/security/configuration/guide/scfike.html
Encryption algorithm
56-bit DES-CBC, des, Default 56-bit DES-CBC
168-bit DES, 3des, Default 168-bit DES
Hash algorithm
SHA-1 (HMAC variant), sha, Default SHA-1
MD5 (HMAC variant), md5
Authentication method
RSA signatures, rsa-sig, Default RSA signatures
RSA encrypted nonces, rsa-encr
preshared keys, pre-share
Diffie-Hellman group identifier
768-bit Diffie-Hellman, 1, Default 768-bit Diffie-Hellman
1024-bit Diffie-Hellman, 2 Lifetime of the security association

Any number of seconds, Default 86400 seconds (one day)