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.