What Is the Usual Way to Gain Command Line Access

What is the usual way to gain command line access to computing instances in an IaaS cloud?

A) By providing a public SSH key to the cloud management system and using the matching private SSH key to log into the instances.
B) Usually computing instances are accessed through a web frontend and do not allow command line access.
C) By either telnet or SSH using the credentials of the cloud management system account with administrative privileges.
D) By using a telnet session with the credentials set and publicized by the creator of the computing instance's system image.
E) By using a VNC console which does not require authentication when it is invoked via the cloud management system.