A sound wave from a jackhammer travels through a section of concrete with a fixed frequency. At the concrete's boundary is mud. The diagram below shows the path of the sound wave as it travels from the concrete into the mud. What happens to the sound wave when it passes from the concrete into the mud? A. Its direction and speed remains the same. B. Its direction and speed changes. C. Its direction changes but speed remains the same. D. Its direction remains the same but speed changes.