As in the program Only Connect, you have to find the connection between four things, which appear one at a time. All four are now below.
M1 Junction 3
Yorkshire South Riding
The year zero
The connection is that all of these have been missed out.
There are Vitamins B1-B3 and B5-B7, but no B4
Junction 3 on the M1 was never built and they go from 2 to 4.
There were three Ridings of Yorkshire - North, East and West - but no South.
And there is no year zero, the years go from 1 BC to 1 AD.