Correct Answer: The policeman said to us, "Do not block the traffic."

Solution : The fourth option is the correct choice.

The given sentence is indirect speech. The steps for changing or converting indirect speech into direct speech are:

• The reporting verb "said" is changed to "warned " in the direct speech.
• "Do not" is used as a command or entreaty not to do something.
• In this case, there's no need to adjust pronouns, but the form "not to block" is changed to "do not block".
• The words of the speaker are enclosed in the inverted commas.

Hence, the correct answer is: The policeman said to us, "Do not block the traffic ."