Directions: Choose the best alternatives from the given options to fill up the blanks.

Police ______ the plans for a mass _______ by University students, who were waiting outside Vidhan Sabha to hold up the Chief Minister's car.

To prevent from accomplishing a purpose is to thwart them. Demonstration is a public exhibition of the attitude of a group of persons toward a controversial issue, or other matter, made by picketing, parading, etc. This is the correct option in this context as the police prevented the University students from protesting against something as the reference is to holding up the chief minister's car. The phrase 'hold up' means to forcibly delay or stop someone.