In a series circuit, all of the components are connected in the same 'loop' and the current only has one direction/path it can flow through.
In the first three options, the current has multiple paths it can go through. So these three circuits are parallel and not series.
In the last option, the current only has one path where it can flow through, so that circuit is in series.
So Circuit <u>D </u>is a series circuit.
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Answer
Circuit D
This is due to the tilt of the earth on its axis. Although the Sun shines on Earth, because of how the Earth is tilted, the equator is more directly hit compared to places found on the poles. The poles are hit at an angle, therefore the sunlight they receive is lesser than the places at the equator.