Which of the following could replace 'crucial' as used in the passage?

Directions: Read the following passage carefully and select the most suitable option according to the corresponding number in the passage.
The economic development of every state largely (1) depends on how its energy requirements are satisfide (2). Not a single branch (3) of modern material production can do (4) without energy. Fuel and power are crucial (5) for overall scientific and technological progress. As a matter of fact, per capita (6) fuel–and–energy consumption (in particular, that of electric power) is one of the basic indicators (7) of this progress. Such key (8) areas as electrification, mechanisation and automation require an increasing amount of electric power.