The correct option is B I have been advised to consume only leafy green vegetables for a couple of days.
An adjective is usually placed before the noun it modifies.
The
underlined adjective "green" is an adjective of colour, it must be placed
before the noun it qualifies, i.e., "vegetables". This is not seen in the
given sentence, hence option A is incorrect. The correct placement is seen in C, hence the right option is C.
Option B is incorrect because the adjective is placed after the entire sentence, whereas it must be placed close to the noun it modifies.
Option D is incorrect because the adjective 'green' must be placed after the other adjectives (only: adjective of quantity, leafy: adjective of quality) that come in the order: quantity, quality, colour.