1. **State the problem:** Calculate the value of $|7 - 3| - |3 - 7|$. 2. **Recall the absolute value definition:** The absolute value $|a|$ is the distance of $a$ from zero on the number line, always non-negative. 3. **Calculate each absolute value:** $$|7 - 3| = |4| = 4$$ $$|3 - 7| = |-4| = 4$$ 4. **Subtract the two values:** $$|7 - 3| - |3 - 7| = 4 - 4 = 0$$ 5. **Final answer:** The expression evaluates to $0$. Therefore, the correct choice is D. 0.