**Core Concept**
The human brain exhibits greater intelligence compared to the monkey brain primarily due to its larger size and more complex neural organization. This increased brain volume allows for a greater number of neurons, synapses, and neural connections, enabling more complex cognitive processes.

**Why the Correct Answer is Right**
The larger size of the human brain is directly correlated with increased cognitive abilities, as it provides a greater surface area for neural connections and a higher concentration of neurons. This is reflected in the higher brain-to-body mass ratio in humans, which is approximately 2%, compared to 1% in monkeys. The increased cerebral cortex volume in humans, particularly in the frontal, parietal, and temporal lobes, is also responsible for the enhanced cognitive capabilities.

**Why Each Wrong Option is Incorrect**
**Option B:** Increased convolutions alone do not account for the superior intelligence of the human brain, as both humans and monkeys exhibit complex folding patterns in their cerebral cortices. However, the human brain has a more extensive and complex convolutional pattern, which is not the primary reason for its intelligence.
**Option C:** While the brain-to-body surface area ratio is indeed higher in humans, it is not the primary factor contributing to human intelligence. This ratio is more of a byproduct of the larger brain size rather than a direct cause of intelligence.
**Option D:** Increased blood supply to the brain is essential for its function and survival, but it is not the primary reason for the human brain's superior intelligence. The brain's high metabolic rate requires a significant amount of oxygen and glucose, which is supplied by the blood, but this is a support mechanism rather than a contributor to intelligence.

**Clinical Pearl / High-Yield Fact**
The brain-to-body mass ratio is a useful indicator of cognitive abilities, with higher ratios generally corresponding to increased intelligence. However, it is essential to note that this ratio does not solely determine intelligence, and other factors such as neural organization and synaptic plasticity also play critical roles.

**✓ Correct Answer: A. Larger brain**