Tyrone and Valerie wanted to determine what feature of a paper airplane would cause it to fly the farthest. Tyrone made his airplane with longer wings than Valerie's airplane. Valerie's airplane had shorter wings than Tyrone's. After testing the two airplanes several times, the data shows that wider wings help airplanes fly farther than shorter wings.

Which characteristic of science is missing from this experiment?

The question is not testable because paper airplanes are always changing.
The phenomenon is not observable because air resistance changes.
The experiment is not replicable because controlled variables are not included.
The results are not reliable because the airplanes were only tested one time.