问题：

[单选] 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.the Company.com contains an exchange server 2010 client access server named -ex13.The mobile clients at Company.com are configured to either run windows mobile 5.0， windows mobile 6.1 or windows mobile 6.5.the mobile users use the internet to connect to -ex13， using mail.Company.com.you have received instructions from the cio to equip -ex13 with a certificate.however， the mobile users need to connect to -ex13 from the internet via exchange activesync.What should you do？（）

A . You should consider including Company.com in the certificate.
B . you should consider including -ex13.Company.com in the certificate.
C . You should consider including EAS.Company.com in the certificate.
D . You should consider including mail.Company.com in the certificate.