When all switches are connected to each other, you need to enable trunking on switch B so that users can ping each other. You can also convert them to a big collision domain so that users on each switch can talk to each other.
for as long as there are two or more vlans in a switch, its interface connected to anoother switch or device <not a host or a PC> must be configured as a trunk. if one is configured as a trunk and other is not, there will be incompatibility.
If you configure the interface connection between the 3 switches as a trunk, it can deinetely communicate.