The correct answer is - A. hydroelectric.
Canada is a country that has lot of rivers, lakes, and a vast coastline, all of which enables the country to use the water as its prime source for production of electricity. In fact, more than half, 60.1% to be more precis, of the total electricity production comes from the water sources, thus the dominant one is the hydroelectricity.
All the other sources for production of electricity combined are producing less then the hydroelectric power, with the nuclear power being second with little more than 15%, and the natural gas and the coal each accounting for around 10% of the total production of electricity in the country.