Ahydrogen fuel cell is more efficient than a combustion reaction because very little of the released energy is released as when used at home, a fuel cell eliminates the need for the cell is portable.
options for the first blank are
heat
electrical energy
chemical energy
options for the second blank are
oxygen
hydrogen
electrical grid

Answer;

-Heat

-Electrical grid

-A hydrogen fuel cell is more efficient than a combustion reaction because very little of the released energy is released as heat. When used at home, a fuel cell eliminates the need for electrical grid because the cell is portable.

Explanation;

-Fuel cells generate electricity by an electrochemical reaction in which oxygen and a hydrogen-rich fuel combine to form water. Unlike internal combustion engines, the fuel is not combusted, the energy instead being released electrocatalytically.

-Fuel cells have a number of benefits compared to combustion reactions; Fuel cells have a higher efficiency than diesel or gas engines, most fuel cells operate silently, compared to internal combustion engines, and they can eliminate pollution caused by burning fossil fuels; for hydrogen fueled fuel cells, the only by-product at point of use is water.

your answer would be a, maximum exploitation of resources.