Explanation:

The correct option is (D) in the disk drive. When referring to inserting a 'disk' into a computer, it typically means a removable storage medium such as a floppy disk, a CD, or a DVD. These types of disks are physically inserted into a dedicated hardware component called a 'disk drive' (e.g., a floppy disk drive, CD-ROM drive, or DVD drive) which reads data from or writes data to the disk. Option (A) in the modem is incorrect; a modem is a device for network communication. Option (B) in the hard drive is incorrect; a hard drive is an internal, non-removable storage device, and you do not 'put' a disk into it in the sense of insertion. Option (C) into the CPU is incorrect; the CPU (Central Processing Unit) is the processing unit of the computer and does not accept disks.