Correct Answer: My sister said, "Let us go for a walk in the fresh air."

Solution : The correct option is the fourth option.

Direct speech involves quoting the exact words spoken by someone. When converting a sentence from indirect to direct speech, you generally:

• The reporting verb "suggested" is changed to "said". and the sentence should begin with let which is used in a sentence to express a suggestion or proposal .
• The connector "that" is removed.
• There would be no change in the reported clause because it is in the present tense.
• The words of the speaker are enclosed in the inverted commas.

Therefore, the converted sentence in direct speech would be: My sister said, "Let us go for a walk in the fresh air".