The three main elements are:
FUEL, for solid or liquid engines. This is the part that actually burns.
OXIDIZER, for both, as there is not enough oxygen in the fuel cell to cause combustion....
Well, a typical "he" will be male. In human, this means that "he" will produce hormone testosterone and not estrogen which is what "she" will produce. Also, "he" will not have a mammary glands...