The correct answer is D) bimetallic strip detector. Bimetallic strip detectors are more prone to false alarms compared to the other fixed temperature heat-actuated fire detectors listed. This is because bimetallic strips are sensitive to ambient temperature changes, which can cause the strip to bend and trigger the alarm even in the absence of an actual fire. In contrast, fusible metal, liquid expansion, and snap-action bimetallic disc detectors are generally less affected by ambient temperature fluctuations and are more reliable in accurately detecting fire conditions.