EWS 15: Clause with "so"

Siew Peng was hungry.

She ate two slices of bread.
Siew Peng was hungry so she ate two slices of bread.
She felt thirsty after that.
She felt thirsty so she drank a glass of water.
I have been playing football the whole afternoon so I am feeling hot.
I am hot so I am sitting under the fan.
I have left the windows open so that there will be more fresh air.