The correct answer is: B. on the primary IDE.
An ATA CD-ROM drive is a type of optical drive that uses the ATA (AT Attachment) interface to connect to a computer. The ATA interface is a standard interface for connecting storage devices to computers, and it is used by many different types of storage devices, including hard drives, floppy drives, and CD-ROM drives.
The primary IDE bus is the first IDE bus on a computer. It is typically used to connect the primary hard drive, but it can also be used to connect other storage devices, such as a CD-ROM drive.
The secondary IDE bus is the second IDE bus on a computer. It is typically used to connect the secondary hard drive, but it can also be used to connect other storage devices, such as a CD-ROM drive.
The SCSI bus is a different type of bus that is used to connect storage devices to computers. SCSI is a more advanced bus than ATA, and it supports faster data transfer rates. However, SCSI is also more expensive than ATA.
Therefore, the correct answer is: B. on the primary IDE.