Passwords must not be sent through email in plain text. Passwords must not be stored in plain text on any electronic media. It is acceptable to store passwords in a file if it is encrypted with PGP or equivalent strong encryption (once again depending on your organization policy). All vendor supplied default passwords must be changed.

Explanation/Reference:
Explanation:
Digital Signal Level 1 (DS - 1) provides 1.544 Mbps over a T1 line.
Incorrect Answers:
A: Digital Signal Level 0 (DS - 0) provides from 64 Kbps up to 1.544 Mbps on a Partial T1 line.
C: There is no framing specification named DS-2.
D: Digital Signal Level 3 (DS - 3) is a specification for T3, not for T1.
References:
Stewart, James M., Ed Tittel, and Mike Chapple, CISSP: Certified Information Systems Security Professional Study Guide, 5th Edition, Sybex, Indianapolis, 2011, p. 165

Explanation
WS-Trust
The protocol used for issuing security tokens is based on WS-Trust. WS-Trust is a Web service specification that builds on WS-Security. It describes a protocol used for issuance, exchange, and validation of security tokens. WS-Trust provides a solution for interoperability by defining a protocol for issuing and exchanging security tokens, based on token format, namespace, or trust boundaries.
Reference: https://msdn.microsoft.com/en-us/library/ff650503.aspx