Root -cause (a plant or cutting) to grow roots/ establish deeply and firmly.
Rot - (chiefly of animal or vegetable matter) decay or cause to decay by the action of bacteria and fungi; decompose.
Route - a way or course taken in getting from a starting point to a destination.
Riot - a violent disturbance of the peace by a crowd.
Among the given options, only 'route' fits in the blank contextually and implies the question which asks about the way taken/used by the minister to reach the assembly.
The correct sentence is: Which route does the minister take to reach the Assembly?
Hence, option (c) is the answer.