No one thought of anything even a little bit like the zipper until Whitecomb L.Judson

came along. There were buttons and button-holes, hooks and eyes, laces and buckles. They all took an irritatingly long time to do up, especially when men wore high-laced boots and fashionable ladies squeezed themselves into long corsets. Whitecomb L.Judson’s slide-fastener was an out-of-the-blue invention, and no one knows what gave him the idea. No one even knows much about him, except that he was a mechanical engineer living in Chicago and that he patented other inventions, to do with a street railway system and motor-cars. Judson invented the first zipper(called, at the time, a Clasp Locker or Unlocker)in 1891. This ingenious little device looks so simple, and the principle behind it is simple: one row of hooks and eyes slotting neatly into another row by means of a tab. Yet it took 22 years, many improvements and another inventor to make the zipper really practical.

The word "ingenious" means ()

A、clever

B、admirable

C、important

D、useful