Why did the western front bog down with little movement?

Technology changed everything. The creation of machine guns led to trench warfare. This style of warfare meant that armies didn't move as they once had on maps. There was also the use of chemicals such as mustard gas. If you fled or retreated, it could take months or years to take back the few feet that you gave up. 

Ithink it's f if it's not then it is c a