Q15. Which of the following is an appropriate description concerning the OS for PCs?
a) Only one type of OS can be installed and executed on one PC.
b) There is no OS for PCs that are equipped with a 64-bit CPU.
c) When an OS is upgraded to a new version, any software operating with the old
version of the OS can no longer be used.
d) There exist some OSs for PCs that can be started up by using an external storage
device, such as a CD-ROM and USB memory, other than the hard disk.