The soldiers are issued (infrared) goggles to them see in the dark.
a. outside visible spectrum
b. creating light by radiating heat
c. emitting light by creating water vapor
d. producing light by adding electrons to a glowing material

Option B: Creating light by radiating heat.

Even under very dark conditions, there is little bit of light present. Some of it can not be visible to naked eyes as it may be infrared. Infrared goggles are used to collect the available light and amplify it to see it in the dark. Every hot object including human body, emit heat in the form of IR light, using thermal capturing techniques, infrared goggles capture this infrared light making the object visible in dark.

Therefore, creation of light by radiating heat helps the soldiers to see in the dark.