LONG BEANS Dau gok
'Long' means 1-3 feet in length. They come in two colors: light green, known as baak dau gok or 'white long beans', and dark green, known as cheng dau gok or 'green long beans'. Because they are small and round in cross-section and so long, they actually look more like string than the short beans that Americans have named 'string beans'. (The Cantonese call this latter stringy bean yook dau.
The darker ones are considered superior, but let personal preference and intended use guide your purchase. In both cases, the smaller the swellings (i.e. beans growing inside) and the firmer the pod, the crunchier the texture and the sweeter the flavor.
The dark green ones have a thin tight pod wall and remain crunchy when cooked. The lighter green ones have a thicker wall, which is more succulent when young, but flabby and fibrous when old. (Podded beans are considered good summer fare.)