Réponse :

a)They will ask you to open your cases.

b)Somenone stole my bicycle.  

c)They do not allow dogs in that shop.

d)They might have sold the flat.

e)If the girls had seen the accident.

f)They will certainly reduce taxes soon.

g)They are going to repair the bridge.

a) The case will be asked to be opened by them.

b)My bicycle got stolen by someone.

c)In that shop, dogs aren't allowed.

d)The flat might have been sold.

e)If the accident had been seen by the girls.

f)Soon, the taxes will be reduced by them.

g)The bridge will be repaired by them.

Explications :

Dans le premier j'ai soulignez les sujets et dans le deuxiemes je les-ai mis au passif.