The correct answer is: A. Upright
A pyramid of numbers is a graphical representation of the distribution of individuals by age or stage in a population. In an upright pyramid, the number of individuals decreases with increasing age or stage. This is because more individuals are born than die at each stage, so the population pyramid is wider at the bottom and narrower at the top.
An inverted pyramid is a graphical representation of the distribution of individuals by age or stage in a population in which the number of individuals decreases with decreasing age or stage. This is because more individuals die than are born at each stage, so the population pyramid is narrower at the bottom and wider at the top.
A spindle-shaped pyramid is a graphical representation of the distribution of individuals by age or stage in a population in which the number of individuals is relatively constant across all ages or stages. This is because the number of births and deaths are approximately equal at each stage, so the population pyramid is approximately the same width at all levels.
In a single tree, the pyramid of numbers is upright because there are more young trees than old trees. This is because trees typically live for many years, so there are always a large number of young trees being born and a small number of old trees dying.