Gravity, Gas, Nitrogen, Carbon Dioxide, and Many Gases.
Asterioids
iron
nickel
Answer: a. testing effect
Explanation:
Testing effect is a type of threat to internal validity of an experiment. Internal validity is assessing whether a factor makes a difference in an experiment or not and if it does, whether there is adequate evidence to support this correlation.
Testing as a threat to internal validity is when a second test is taken on the outcome of a first test. Other internal validity threats are history, maturation, instrument modifications.
It's hard for me to make out what is all in the photograph because it's grainy, so hopefully this still helps!
