Special considerations must be given to systems using liquid hydrogen for fuel because of: a. liquid hydrogen's low density b. liquid hydrogen's low storage temperature c. the high flammability of hydrogen vapors d. all of the above

D.All of the above

Explanation:

Properties of hydrogen:

1.It is lighter than air.It has density about 0.089 g/L.

2.Hydrogen  rapidly change from liquid state to gas,so special protection is required to protect it.

3.It is highly flammable gas.

4.Liquid form of hydrogen exits at -432 F .This is very low temperature so special protection requires to keep it in liquid form.          

the warning light flashes for a second or two when the engine starts. if it stays on, there's must be something wrong with the coolant. you should never dare to continue driving when the light is on. pull over as soon as possible and shut the engine off.

hope this is what you're talking about