根据以下材料，回答
Using a computer or smartphone at nightcan cause us to 11 on the pounds, new research has revealed.
The study found a link between blue light 12 --blue light is 13 by smartphones and tables--and increasedhunger. It found that exposure to the light increases hunger levels for severalhours and even increases hunger levels 14 eating a meal.
Results of the US study show thatblue-enriched light exposure, compared with 15 light exposure, was 16 with an increase in hunger that began 15minutes after light onset and was still present almost two hours after themeal. Blue light exposure has also already been shown to decreased 17 in the evening, increasing the risk ofinsomnia.
Study co-author Ivy Cheung, of NorthwesternUniversity in Chicago, said, "A single three-hour exposure toblue-enriched light in the evening 18 impacted hunger andglucose metabolism." "These results are important because theysuggest that 19 environmental light exposure for humansmay represent a novel 20 of influencing food intake patterns andmetabolism."
The study group 21 10 healthy adults with regular sleep and eating schedules who received
22 carbohydrate-rich meals. They completed afour-day trial 23 dim light conditions, which involvedexposure to less than 20 lux during 16 hours 24 and less than three lux duringeight hours of sleep. On day three they were exposed to three hours of 260 lux,blue-enriched light starting 10.5 hours after waking up, and the effects werecompared with dim light exposure on day two.
Ms Cheung said more research is needed todetermine the 25 of action involved in the relationshipbetween light exposure, hunger and metabolism.
A.after
B.before
C.during
D.when