Which of the following lines in /etc/fstab mounts the device /dev/cd0a to /cdrom?

The /etc/fstab file contains information about the file systems that are mounted automatically at boot time or by the mount command. The file has six fields separated by whitespace: device, mount point, file system type, mount options, dump frequency, and pass number. The correct answer is D because it specifies the device (/dev/cd0a), the mount point (/cdrom), the file system type (cd9660), the mount option (ro for read-only), and the dump frequency and pass number (both 0 for no backup or fsck). The other answers are incorrect because they either have the wrong syntax, the wrong order of fields, or the wrong file system type. References:

BSD Specialist Exam 702 Objectives, Topic 715: Basic Unix Skills, 715.2 File and Directory Management

FreeBSD Handbook, Chapter 3: FreeBSD Basics, 3.8.2 Mounting and Unmounting File Systems