while looking at a graph, you notice a period of time where the line is perfectly horizontal what is most likely taking place during this time period

The correct answer would be - the y-axis variable is constant.

Explanation:

In a normal line graph, there are generally two variables on two different axis one is at the x-axis and the other is on the y-axis that represents the correlation between these two variables. If there is a change in the variable present on the x-axis the change on the variable on the y-axis establishes the relationship among these variables.

If there is a period on the graph where the line is completely horizontal it means the variable present on Y-axis has no change during this period or is constant. Suppose a graph is plotted between speed or velocity on the Y-axis. A perfectly horizontal line on this graph means that speed is not changing over time and remain at te same speed.

organ system-an organ system is a group of organs that work together to perform one or more functions. each does a particular job in the body, and is made up of certain tissues.

unicellular organisms, like bacteria, are able to perform all life functions within one single cell. multicellular organisms need many different types of cells to carry out the same life processes. each of these special types of cells has a different structure that it perform a specific function.