Final answer:
The true statement is B. The absolute value of a number is always positive. Absolute value measures distance from zero, which is a non-negative quantity, making other statements incorrect.
Step-by-step explanation:
The statement that is true is: B. The absolute value of a number is always positive. Absolute value refers to the distance of a number from zero on the number line, without considering direction. This distance is always a positive quantity or zero (in the case of the number itself being zero).
For example, the absolute value of -5 is 5, and the absolute value of 5 is also 5. When we consider the sign of a number, by convention, a positive sign indicates that it is greater than zero, and a negative sign indicates that it is less than zero. The opposite of a number is the same magnitude with an inverted sign, not necessarily always positive nor always negative. So, the statement A. The absolute value of a number is always negative is false because absolute values are never negative. Similarly, statements C and D about the opposite of a number always being negative or positive, respectively, are incorrect since the opposite sign depends on the original sign of the number.