Practice question

Arterial PCO2 (B) is the right choice. This sits at the heart of Respiratory System; Exchange of Gases: 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 Arterial PCO2 does in Respiratory System; Exchange of Gases. That reasoning supports Arterial PCO2. 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 Arterial PCO2 from memory, then reveal the letter — that habit builds real recall for Respiratory System; Exchange of Gases.