Question

what brings a sudden change in the environment
a.formation of river
b.formation of mountain
c.gowth of a plant
d.rainfall

Answer 1

Talking about a sudden change in the environment, factors like formation of river, formation of mountain or the growth of a plant cannot be considered in the same magnitude.

All these phenomenon being time consuming and taking place over a prolonged period of time, we are left with rainfall, which indeed causes a sudden change in the environment.

Answer 2

d. rainfall...............