Concept:Continuous variation is a type of variation in which individuals show a range of intermediate phenotypes between two extremes.
Explanation:Continuous variation is controlled by multiple genes called polygenes, and it can also be influenced by environmental factors.
These traits do not fall into separate, distinct categories.
Instead, they show a smooth, graded series of values within a population.
Height in humans is a classic example because people range from very short to very tall, with many intermediate heights in between.
Human blood groups, sex difference, and haemoglobin types are examples of discontinuous variation because they produce clear, separate classes without intermediate forms.
Answer:D. Height in humans