In a Time Series Design,the Series of Observations Before Treatment

Multiple Choice

In a time series design,the series of observations before treatment helps reduce threats to internal validity because

A) a series of observations is more reliable than a single observation.
B) a series of observations has more validity than a single observation.
C) if an outside factor is influencing the scores,the effects should be seen before the treatment is administered.
D) if an outside factor is influencing the scores,it can be stopped before the treatment is administered.