The answer is (B) Hunger.
'X' points to the medulla (hind-brain), which controls involuntary actions — blood pressure, salivation, and vomiting. Hunger is controlled by the fore-brain.
Source: Chapter 6, Section 6.1.2 Human Brain
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The passage explicitly states: "All these involuntary actions including blood pressure, salivation and vomiting are controlled by the medulla in the hind-brain." It also states that the sensation of hunger is associated with "a centre… in a separate part of the fore-brain." So hunger is the odd one out — eliminate it as the answer. In MCQs like this, identify which option belongs to a different brain region than the one labelled.