having a lesser value by a process of depletion
I believe the answer is A.
Hope this helps! ^^
There's a lot of capillaries in the lungs because the blood needs to be transferred and the capillaries are the smallest vessels that can do this.
I think the correct answer would be because copper has a lower activity than hydrogen and cannot replace the bonds in it. Substances that are not oxidizing do not react with copper since the redox potentials are very low. Hope this answers the question.