Adele was appointed an MBE in the 2013 Birthday Honours.
MBE stands for Member of the Order of the British Empire, one of the grades within the United Kingdom's honours system. Adele was recognised as Adele Adkins, her birth surname, for services to music.
The 2013 Birthday Honours were announced in June during Queen Elizabeth II's official birthday celebrations. Adele later received the insignia at Buckingham Palace from Prince Charles in December 2013, making the honour a visible part of her growing public recognition.
The other options are different grades: OBE means Officer, CBE means Commander, and DBE means Dame Commander. Adele received the lower-ranking MBE rather than one of those titles, so “MBE” is the precise answer.