Sentence:  It is the gait of the human who must run to live : arms dangling , legs barely swinging over the ground , head hung down and only occasionally swinging up to see the target , a loose motion that is just short of stumbling and yet <WSD>is</WSD> wonderfully graceful . 
Meaning of the word marked with <WSD> tags:  have the quality of being; (copula, used with an adjective or a predicate noun)