1. The test was too difficult for them to do -> It was such a difficult test for them to do.

2. Someone has left this purse in the classroom -> this purse has been left in the classroom.

3. He can't buy this car because it is very expensive -> if this car weren't very expensive, he could buy it. 

4. Their dog is so fierce that no one dares to come near the house -> they have such a fierce dog that no one dares to come near the house.

5. He turned off the lights and then went to bed -> after turning off the lights, he went to bed.

1. The tes wasn't easy enough for them to do.

2. This purse has been left in the classrom.

3. If he has a lot of money, he can buy this car.

4. They have such a fierce dog that no one dares to come near their house.

5. After having turned off the lights, he went to bed.