Six nutrients needed by human body: protein, sugar, oil, vitamins, inorganic salts and water; Combined with the meaning of the question, rice is rich in starch and belongs to sugar; Beef, egg soup, prawns and fish contain oil, protein and inorganic salts, indicating that the vitamin content in food is less; Therefore, in order to make the nutritional collocation more reasonable, it is necessary to supplement foods rich in vitamins.

A steamed stuffed bun is rich in starch (sugar) and protein. The option is wrong.

B, pork is rich in protein, so the option is wrong.

C, milk is rich in protein, so the option is wrong.

D, vegetables are rich in vitamins, so the choice is correct.

So choose D.