Help the detective complete her formal report on the great penguin heist by choosing the correct prepositional phrase for each clause.

The exact extent to which the zookeeper was involved remains a heavily guarded secret. Furthermore, the absurd premise on which the entire heist was based makes absolutely no logical sense. Finally, the highly suspicious manner in which the penguin vanished suggests a mastermind at work.

The exact extent to which the zookeeper was involved remains a heavily guarded secret.

We use "to which" because the standard phrase is "the extent to something."

Furthermore, the absurd premise on which the entire heist was based makes absolutely no logical sense.

We use "on which" because we "base something on a premise."

Finally, the highly suspicious manner in which the penguin vanished suggests a mastermind at work.

We use "in which" because things happen "in a certain manner."