Directions: In each of the following sentences, a sentence is given with certain words in bold. Choose the pair/s of such words which need to be interchanged so as to make the sentence grammatically correct and meaningful.

Nature provides ecosystem (A) services, but these are often not included in productivity absorption (B) they are vital for food production, for clean air and water, provision (C) of fuel for millions, estimates (D) of carbon in the atmosphere, and climate moderation.