A body moving with constant speed in a straight line means its velocity is constant (both magnitude and direction are unchanging). This type of motion is defined as uniform motion.

A body moving with constant speed in a straight line means its velocity is constant (both magnitude and direction are unchanging). This type of motion is defined as uniform motion.

• a) Accelerated motion involves a change in velocity (either speed or direction).
• b) Uniform motion means constant velocity, which includes constant speed in a straight line.
• c) Circular motion involves a continuous change in direction, even if the speed is constant, meaning it is accelerated motion.
• d) Random motion implies unpredictable changes in speed and/or direction.

Therefore, the correct option is (b).

The final answer is $\boxed{\text{B}}$