What Does "Seasonal Adjustment" Mean

Multiple Choice

What does "seasonal adjustment" mean?

A) Data are seasonally adjusted if we take out changes that occur in about the same size and same time every year.
B) Data are seasonally adjusted when we ignore the effects of one-time events such as strikes and hurricanes.
C) Data are seasonally adjusted if we report the average for this month over several past years, not just this one month's data.
D) Data are seasonally adjusted if we report the average for the past four months, not just this month's data.