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. I must help him.

He must helped by me.
I must held him.
He must get help from me.
He must be helped by me.

Answer: Option D

Explanation:

If we have "Subject + Modal Auxiliary verb + first verb + object"
then we change it to

Passive subject + Modal Auxiliary verb + be + third form + by + passive object.

Modal Auxiliary verb are : can, could, shall, will, may, might, should, would, must, ought to etc.

2. Post this letter.

Let this letter be post.
Let this letter be posted.
Let this post be letter.
Let this letter is posted.
Let this letter are posted.

Answer: Option B

3. Let us play.

It is suggested that we could play.
It is suggested that we should play.
It is suggested to play.
No change

Answer: Option B

Explanation:

When we use "us" after "Let", it means it is a suggestion. So it is converted as this example.

4. We ought to have saved our environment.

Our environment ought to had been saved.
Our environment ought to have been save.
Our environment ought to have been saved.
Our environment ought to have saved.

Answer: Option C

5. 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.