A man has to plant exactly four varieties of flowers in a flower bed in his garden, one variety in each of the four rows, in an ascending order of height from the first row to the fourth row. The seven varieties available to the man, in ascending order of height, are red begonias, pink petunias, orange marigolds, red geraniums, white snapdragons, yellow zinnias and pink cosmos. The following restrictions on color arrangements apply: No two varieties of the same color can be planted. Orange flowers cannot be planted in a row immediately adjacent to a row of yellow flowers. Flowers of which of the following colors CANNOT be planted in the third row?