What is used to avoid assigning entire addresses of a particular class to networks that didnâ’t have that many hosts?

CIDR (Common Internet Domain Routing). Originally, there were Class A, Class B, Class C and Class D networks. Class A nets had an 8 bit netmask, so they could have 17+ million nodes (whatever 2^24 is). Class B networks had a 16 bit netmask and a  capacity of 65,536 nodes. Class C nets 24 bit netmask, 256 nodes. Class D was usually (I think, lot of cobwebs) 26 bit, 64 node.

When internet numbers started to run low, the protocols were tweaked to accept variable length netmasks, CIDR.

You need to call the office. and then you need to give them a reason on why you want to change your username.

In windows explorer, select the file, folder, or groups of files and folders you'd like to copy. you can select multiple files or folders in several ways: click the first file or folder you want to select, hold down the ctrl key, and then click each additional file or folder you want.