Can anyone tell me that how these sentences are converted into active voice?

1. Alice was not much surprised at this.

2. He will be greatly surprised if he is chosen.

3. The streets were thronged with spectators.

Please help me!
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These sentences cannot be made passive because none of the verbs are used in the transitive sense. That is, none of them have direct object.

Alice was suprised -- no direct object.

This surprised Alice. -- Alice is the direct object of "this" so you could make it passive by saying "Alice was not surprised by this." However, your sentence has Alice surprised AT something, a non-transitive sense of the word 'surprised."
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Ok Thanks!

Sometime we commit the subject in the active form when it is not necessary. For example they .people someone, it etc . So the Active form is

It will surprise him greatly if he chooses.