What is required for a sound wave to be reflected? A. A sound wave with frequency equal to the natural frequency of the object
B. An obstacle for the wave to bend around
C. A hard surface for the wave to bounce off
D. A change in frequency as the wave enters another medium

Iknow the answer to 13 is b and 14 is d. i just need to know why the correct answers are correct

Miner's coal distributors does not mine coal itself, nor does it even store or handle the coal. instead, miner's solicits orders for low sulfur coal from other firms, then purchases the required amount from suppliers and directs them to ship the coal to its customers. what is miner's

Light waves can move through , but they travel fastest when they move through a(n) .