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; Peanut, fried beef, steamed fish and milk 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, spicy tofu is rich in protein, so the option is wrong.

B scrambled eggs are rich in protein, so the option is wrong.

C, cold cucumber is rich in vitamins, so the choice is correct.

D, braised pork ribs are rich in protein, so the option is wrong.

So choose C.