Information:  - Leaf vegetables, also called potherbs, greens, vegetable greens, leafy greens, or salad greens, are plant leaves eaten as a vegetable, sometimes accompanied by tender petioles and shoots. Although they come from a very wide variety of plants, most share a great deal with other leaf vegetables in nutrition and cooking methods.  - Beijing (formerly romanised as Peking) is the capital of the People's Republic of China and the world's third most populous city proper. It is also one of the world's most populous capital cities. The city, located in northern China, is governed as a direct-controlled municipality under the national government with 16 urban, suburban, and rural districts. Beijing Municipality is surrounded by Hebei Province with the exception of neighbouring Tianjin Municipality to the southeast; together the three divisions form the Jingjinji metropolitan region and the national capital region of China.  - Chinese cabbage ("Brassica rapa", subspecies "pekinensis" and "chinensis") can refer to two groups of Chinese leaf vegetables often used in Chinese cuisine: the Pekinensis Group (napa cabbage) and the Chinensis Group (bok choy).  - Bok choy or pak choi ("Brassica rapa" subsp. "chinensis") is a type of Chinese cabbage. "Chinensis" varieties do not form heads and have smooth, dark green leaf blades instead, forming a cluster reminiscent of mustard greens or celery. "Chinensis" varieties are popular in southern China and Southeast Asia. Being winter-hardy, they are increasingly grown in Northern Europe. This group was originally classified as its own species under the name "Brassica chinensis" by Linnaeus.  - Plants are mainly multicellular, predominantly photosynthetic eukaryotes of the kingdom Plantae.  - Cabbage or headed cabbage (comprising several cultivars of Brassica oleracea) is a leafy green or purple biennial plant, grown as an annual vegetable crop for its dense-leaved heads. It is descended from the wild cabbage, "B. oleracea" var. "oleracea", and is closely related to broccoli and cauliflower (var. "botrytis"), brussels sprouts (var. "gemmifera") and savoy cabbage (var. "sabauda"). Cabbage heads generally range from , and can be green, purple and white. Smooth-leafed firm-headed green cabbages are the most common, with smooth-leafed red and crinkle-leafed savoy cabbages of both colors seen more rarely. It is a multi-layered vegetable. Under conditions of long sunlit days such as are found at high northern latitudes in summer, cabbages can grow much larger. Some records are discussed at the end of the history section.  - Napa or nappa cabbage ( Brassica rapa subsp . pekinensis or Brassica rapa Pekinensis Group ) is a type of Chinese cabbage originating near the Beijing region of China , and is widely used in East Asian cuisine . In much of the world , this is the vegetable referred to as `` Chinese cabbage '' .  - Brassica rapa L. is a plant consisting of various widely cultivated subspecies including the turnip (a root vegetable); napa cabbage, bomdong, bok choy, and cime di rapa (leaf vegetables); and ("Brassica rapa" subsp. "oleifera", an oilseed which has many common names, including field mustard, bird rape, keblock, and colza).    After reading the paragraphs above, we are interested in knowing the entity with which 'napa cabbage' exhibits the relationship of 'taxon rank'. Find the answer from the choices below.  Choices: - form  - group  - kingdom  - section  - subspecies  - variety
A:
subspecies