Which option completes the text below correctly?

There are cells in the retina of our eye that______ directly with the brain's biological clock regulators located in the hypothalamus and this pathway is most affected by light. These neurons______to be most affected by light waves from the blue spectrum or blue light. This is the kind of light most prominent in electronic lights from computers and smartphones. This______a modern challenge that can adversely affect our natural sleep-wake cycle.

Additional factors that can hamper sleep______ pain conditions, medications for other conditions, and the increased demands and connectedness of modern society.

(Adapted from http://theconversation.com)