In an experiment on the effects of massed versus distributed practice on learning, introductory psychology students who volunteered for extra credit were randomly assigned to one of two groups. Both groups were to practice a perceptual-motor task five times for 10 minutes each. Group 1 did all five 10-minute practice sessions in one evening while group 2 was asked to do one 10-minute practice session a night for five consecutive nights. All of the participants in Group 1 completed the experiment, but only 30% of the participants in Group 2 showed up for all five nights. This study is an example of confounding by .

The correct answer is attrition

Explanation: Attrition occurs when participants leave during a study.

Longitudinal research is a study that provides an understanding of changes  behavior over time. For these studies, it is necessary to  develop a panel of households that will be monitored and researched throughout  of time.

explanation:

allergens: overstimulate the nerve system

neurotics: attack nerve cells

mutagens: damage or otherwise alter dna sequence

generators: cause defects during growth and development  

carcinogens: cause unchecked cell growth

i hope you get the idea according to me these are the effects that happened.

1. artillery

2. jose san martin

3.their economies remained dependent on outside powers.

4. drafted new economies

5. democracies have replaced dictatorships