Answer the following question given this paragraph: 

Waves may reflect off an obstacle that they are unable to pass through. When waves are reflected straight back from an obstacle, the reflected waves interfere with the original waves and create standing waves . These are waves that appear to be standing still. Standing waves occur because of a combination of constructive and destructive interference. You can see animations of standing waves at the URLs below.


Q: What do waves do when they are unable to pass through an object?


A:
reflect off