Suppose that I carried out a study by running all of the participants in my control group in the morning and all of the participants in my experi­mental group in the afternoon. Condition (or level) of...

Suppose that I carried out a study by running all of the participants in my control group in the morning and all of the participants in my experi­mental group in the afternoon.  Condition (or level) of the independent variable would be confounded with:

1. time of day


2. practice on the participants' task


3. length of experience with the independent variable


4. all of the above