Sophie monitored the flask and indirectly determined the amount of liquid that remained in the flask by measuring the amount of liquid that had vaporized, condensed in the glass tube, and collected in a beaker at the end of the tube. Sophie measured the amount of liquid every five minutes until all of the liquid in the flask had vaporized.

Making measurements every five minutes is an example of
A.
data analysis.
B.
systematic observations.
C.
proposing conclusions.
D.
making inferences.