Those familiar with Only Connect will know how this works. but a quick explanation will not go amiss.
You will see three phrases, one at a time. These are now below. You have to work out the fourth phrase.
The three are:
2019 C
2018 É
2016 E
The years refer to the most recent Six Nations Grand Slams, and the letters are the name of the winning country in its own language - C for Cymru (Wales), É for Éireann (Ireland) and E for England (England). The Grand Slam before 2016 was in 2012, which was won by Wales and so the fourth in the sequence is
2012 C