Sentence:  It is made up of tumbling , which might be said to <WSD>start</WSD> with a somersault , run through such stunts as headstands , handstands , cartwheels , backbends , and culminate in nearly impossible combinations of aerial flips and twists and apparatus work . 
Meaning of the word marked with <WSD> tags:  take the first step or steps in carrying out an action