Step-by-step Solution:

\[ \textbf{Question: } \quad \text{Which of the following statements about ASCII and Unicode is correct?} \] \[ \begin{array}{ll} \textbf{A.} & \text{Unicode and ASCII are completely different and share no common characters.} \\[6pt] \textbf{B.} & \text{ASCII uses 16 bits per character, while Unicode uses only 7 bits.} \\[6pt] \textbf{C.} & \text{ASCII can represent more characters than Unicode because it uses fewer bits per character.} \\[6pt] \textbf{D.} & \text{Unicode is backward compatible with ASCII and includes all ASCII characters in its encoding.} \end{array} \] --- \[ \textbf{Analysis:} \] $$\text{A: False — Unicode includes ASCII as a subset }$$ $$\text{B: False — ASCII uses 7 bits (or stored in 8 bits), while Unicode can use 16 bits (UTF-16) or more. } $$ $$\text{C: False — Unicode represents far more characters (over 140,000), ASCII only 128. }$$ $$\text{D: True — Unicode is designed to be backward compatible with ASCII. } $$ --- \[ \boxed{\text{Correct Answer: D. Unicode is backward compatible with ASCII and includes all ASCII characters.}} \]