The main food crops in the Loess Plateau are () A. Wheat B. Corn C. Rice D. Valley.

Historically, the Loess Plateau has long been in a state of semi-agriculture and semi-grazing, with slow economic development and backward industry. Most people who live here live a simple life. The staple food of local residents is miscellaneous grains (millet), followed by wheat, and the dishes are relatively simple, often accompanied by pickles and peppers.

Therefore, choose: d.