ADH increases water permeability mainly in:
DCT and collecting duct (C) is the right choice. This sits at the heart of Excretory System: the wording points straight to what is happening in the tissue or organ system. A useful study habit is to ask what the structure or process is for: the functional job described in the stem is exactly what DCT and collecting duct does in Excretory System. That reasoning supports DCT and collecting duct. One solid sentence about why this works is enough for recall — you do not need a long essay for every MCQ. When you practise, cover the choices first, write DCT and collecting duct from memory, then reveal the letter — that habit builds real recall for Excretory System.
Ref: Animal physiology is Unit 7 of the CSIR NET Life Science Syllabus, covering core body systems. It accounts for roughly 10% of the total marks in Sections B and C.