You work as the enterprise exchange administrator at Company.com.The Company.com network consists of a single Active Directory domain named Company.com.Company.com has an Exchange  Server 2010 organization.Company.com contains an exchange server 2010 server named -sr15 that has the following roles installed： client access， hub transport， and mailbox server.the Company.com also has a windows server 2008 r2 certification authority （ca）.Company.com has merged with another company named Courseware Publishers that contains an internal root C A.You have received instructions from the CIO to install a certificate to create the federated trust as well as to reduce the cost. What should you do？（）

• A、You need to set up a computer certificate request on -sr15； thereafter you should submit the request to a third-party trusted ca
• B、You need to use -sr15 and generate a self-signed certificate
• C、You need to use request a computer certificate from the Company.com.com ca from -sr15
• D、You need to set up a computer certificate request on -sr15； thereafter you should submit the request to courseware publishers ca