You Plant a Seed in a Pot Containing Soil,and Then

You plant a seed in a pot containing soil,and then add water and place the pot under a light.After the seedling emerged,complete with two green leaves,the carbon dioxide levels decreased in the closed chamber.The developing seedling was using which of the following as a source of energy during this time?

A) water from the soil
B) starch from the seed
C) sugars from the soil
D) nutrients from the soil
E) light