Alternative energy sources like solar and wind power
a.
are always available
b.
are only replenished with human intervention
c.
are renewable
d.
are more versatile than fossil fuels

The correct answer for the fill in the blank is A) Are always available and C) Are renewable.

Solar and wind power are the renewable sources of energy. This means that they can be renewed and replenished naturally. The energy from sunlight and  wind that is solar power and wind power never runs off and it is always available.

Thus, option A) and C) are correct for the fill in the blank.

answer; ///i believe that the correct answer is (a) specialized cells)

every el niño cycle is different. every year.