Sentence:  `` <WSD>Speed</WSD> in painting a picture is valid only when it imparts spontaneity and crispness , but unless the artist has lots of experience so that he can control rapid execution , he would do well to take these first sketches and soberly reorder their design to achieve a unified composition . 
Meaning of the word marked with <WSD> tags:  a rate (usually rapid) at which something happens