The Queen of Spades always lies for the whole day or tells the truth for the whole day. Which of these statements can she never say?
A: "Yesterday, I told the truth";
B: "Yesterday, I lied";
C: "Today, I tell the truth";
D: "Today, I lie";
E: "Tomorrow, I shall tell the truth".
If you liked this problem, here is an NRICH task which challenges you to use similar mathematical ideas.