複選題17. Suppose the frequency of occurrence for C is 1, for O is 2, for U is 3, for N is 4, for T is 5, for E is 6, and for R is 7. We create a Huffman tree and find Huffman codes for them. Which of the following are true? (A) The code for T is 101； (B) The code for U is shorter than the code for T； (C) The shortest code is one bit long； (D) The longest code is 4 bits long.