**Core Concept**
In thyrotoxicosis, the body's metabolic rate is elevated due to excess thyroid hormones, leading to increased oxygen consumption. Beta-blockers are often used to control symptoms such as palpitations, tremors, and anxiety by blocking the effects of excess catecholamines on the heart and peripheral tissues.

**Why the Correct Answer is Right**
Beta-blockers, such as propranolol, primarily work by blocking the beta-1 adrenergic receptors in the heart, which reduces heart rate and contractility. However, they do not affect the metabolic rate or oxygen consumption, which is directly influenced by thyroid hormones. The increased oxygen consumption in thyrotoxicosis is due to the direct action of thyroid hormones on tissues, including the heart, liver, and skeletal muscle, and is not influenced by the sympathetic nervous system, which is targeted by beta-blockers.

**Why Each Wrong Option is Incorrect**
**Option A:** Anxiety is a symptom that can be effectively controlled by beta-blockers, as they reduce the peripheral effects of excess catecholamines.
**Option B:** Tremors are also a symptom that can be controlled by beta-blockers, as they reduce the muscle activity caused by excess catecholamines.
**Option C:** Tachycardia, or rapid heart rate, is a symptom that can be effectively controlled by beta-blockers, as they reduce heart rate by blocking beta-1 adrenergic receptors.

**Clinical Pearl / High-Yield Fact**
It's essential to remember that beta-blockers are not a substitute for definitive treatment of thyrotoxicosis, which involves antithyroid medications or radioactive iodine. Beta-blockers are used only to control symptoms while the underlying cause is being treated.

**✓ Correct Answer: D. Oxygen consumption. Beta-blockers do not control oxygen consumption in thyrotoxicosis.**