Through a series of experiments, an American scientist has obtained an understanding of th

e social structure of the most complex of ant societies. The ants examined are the only creatures other than man to have given up hunting and collecting for a completely agricultural way of life. In their underground nests they cultivate gardens on soil made from finely chopped leaves. This is a complex operation requiring considerable division of labor. The workers of this type of ant can be divided into four groups according to size. Each of the groups performs a particular set of jobs.

The making and care of the gardens and the nursing of the young ants are done by the smallest workers. Slightly larger workers are responsible for chopping up leaves to make them suitable for use in the gardens and for cleaning the nest. A third group of still larger ants do the construction work and collect fresh leaves from outside the nest. The largest are the soldier ants, responsible for defending the nest.

To find out how good the various size-groups are at different tasks, the scientist measured the amount of work done by the ants against the amount of energy they used. He examined first the gathering and carrying of leaves. He selected one of the size-groups, and then measured how efficiently these ants could find leaves and run back to the nest. Then he repeated the experiment for each of the other size-groups. In this way he could see whether any group could do the job more efficiently than the group normally undertaking it.

The intermediate-sized ants that normally perform. this task proved to be the most efficient for their energy costs, but when the scientist examined the whole set of jobs performed by each group of ants it appeared that some sizes of worker ant were not ideally suited to the particular jobs they performed.

In which way are the ants different from other non-human societies？

A．They do not need to search for food.

B．They do not need to look for shelter.

C．Individuals vary in social status.

D．Individuals perform. different functions.