Which factor opposes alveolar expansion?
Correct option is B, Surface tension. In Cardiac Cycle and Regulation, the accurate description is Surface tension, and that is what you should commit to memory. Keep the definition tight and the role clear — Surface tension is the option that correctly names the structure, process, or principle asked for in Cardiac Cycle and Regulation. Then Surface tension is the answer you can defend. Check yourself by covering the options and writing the answer first, then matching the letter — that builds confidence. If the wording feels dense, translate it into everyday language first, then map that plain sentence back onto Surface tension.
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.