A. on B. with C, for D. in
A successful time zone shift depends on knowing the exact time to either (13) or avoid bright light. Exposure to light at the wrong time can actually make jet lag worse. The proper schedule (14) light exposure depends a great deal on (15) travel plans.
Data on a specific flight itinerary and the individual’s sleep (16) are used to produce a Trip Guide with (17) on exactly when to be exposed to bright light.
When the Trip Guide (18) bright light, you should spend time outdoors if possible. If it is dark outside, or the weather is bad, (19) you are on an aeroplane, you can use a special light device to provide the necessary light (20) for a range of activities such as reading, watching TV or working.