#periodogram

Question 1: Single choice

The periodogram of a daily sales series has tall peaks at the weekly and biweekly frequencies. You fit a seasonal model (weekly indicators plus Fourier features) and subtract its fitted values. The periodogram of the deseasonalized series has no large values anywhere. What does this tell you?

The model captured the seasonality; no strong periodic part remains1
The model overfit, since a good model leaves the seasonal peaks in the residuals2
The series had no real seasonality, so the peaks came from the trend3
The trend was removed too, because a periodogram measures the strength of trend4

Timed test