The spreading of a mechanical wave into the region behind an obstruction is called what ?

Diffraction occurs whenever a portion of a wavefront is obstructed by some opaque object.

1 a

2 d

3 a

4 c

explanation:

shield volcanos are angry and get mad over the smallest things so much that there heads erupt   pahoehoe and a'a lava. a composite volcano is the poller opposite of a shield volcano. its   peaceful thing and knows how to control its emotions.