Passwords are one of the multiple ways to authenticate (prove who you claim to be) an identity which allows confidentiality controls to be enforced to assure the identity can only access the information for which it is authorized. It is the authentication that assists assurance of confidentiality not the passwords.
“Network security protocols” is incorrect. Network security protocols are quite useful in assuring confidentiality in network communications.
“Network authentication services” is incorrect. Confidentiality is concerned with allowing only authorized users to access information. An important part of determining authorization is authenticating an identity and this service is supplied by network authentication services.
“Data encryption services” is incorrect. Data encryption services are quite useful in protecting the confidentiality of information.
Reference(s) used for this question: Official ISC2 Guide to the CISSP CBK, pp. 407 -520 AIO 3rd Edition, pp. 415 -580