Wrong answer. You answered A but B and D are the correct answers.
It's a bit naughty of us to throw in a trick question but it's a hot topic and we like to promote debate and conversation.
If the casualty is unconscious and not breathing it is better to perform chest compressions than not. This will keep the (already oxygenated) blood pumping around the casualty and help keep them alive. There is no need for rescue breaths. So the ratio would be 30 & 0. However if you feel able to perform rescue breaths then the ratio is 30 & 2.
From the First Aid Manual, revised 10th edition, printed 2016.
“Healthcare professionals and trained first aiders will deliver CardioPulmonary Resuscitation (“CPR”) using chest compressions combined with rescue breaths. However, if you have not had training in CPR or you are unwilling or unable to give rescue breaths, chest-compression-only CPR has been shown to be of great benefit certainly in the first minutes after the heart has stopped.”
If the person is NOT in your support bubble, please always consider your own personal safety first when delivering first aid. Guidance from the Red Cross can be found here
The St John ambulance link below assumes the casualty is NOT in your support bubble.
Specific changes recommended by the Red Cross UK:
"When checking if a person is breathing do not listen or feel for breathing by placing your ear and cheek close to the person's mouth. Look for a rise and fall of their chest or stomach and normal breathing. If you are unsure, assume they are not breathing."
And the Resuscitation Council UK statements are here