The crawling displayed by many embryonic cells in animals involves distinct events. Which of the fol

The crawling displayed by many embryonic cells in animals involves distinct events. Which of the following sequences places these events in correct order? 
A) protrusion at the cell's leading edge, attachment of protrusion, pulling the cell forward, release and retraction of trailing edge 
B) attachment of protrusion, pulling the cell forward, protrusion at the cell's leading edge, release and retraction of trailing edge 
C) release and retraction of protrusion, protrusion at the cell's leading edge, attachment of trailing edge, pulling the cell forward 
D) attachment of protrusion, protrusion at the cell's leading edge, pulling the cell forward, release and retraction of trailing edge 
E) pulling the cell forward, release and retraction of protrusion, protrusion at the cell's leading edge, attachment of trailing edge