Question Detail

They are not picking the flowers.

The flowers are being picked by them.
The flowers is not being picked by them.
The flowers was not being picked by them.
The flowers are not been picked by them.
The flowers are not being picked by them.

Answer: Option E

1. We help the poor.

The poor is helped by us.
The poor are helped by we.
The poor are help by us.
The poor are helped by us..
The poor was helped by us.

Answer: Option D

2. Thief killed him.

He was kill by the thief.
He killed by the thief.
He was killed by the thief.
He was killed.

Answer: Option C

3. Sit down.

You are requested to sit down.
You are ordered to site down.
You are told to sit down.
No change.

Answer: Option B

4. Someone has stolen his book.

His book is been stolen.
His book has been stolen.
His book is stolen.
His book has stolen.

Answer: Option B

Explanation:

Apart from Rule to make active voice of Present Perfect Tense, which is

Passive subject + has/have + been + third form of verb + by + passive object

Please also note that words like, "someone", "somebody", "people", "police", "public" etc are dropped. But in rare cases we can use them if sentence meaning is not clear.