Correct Answer & Explanation
Option D
• An imperative sentence starting with 'Let us' or 'Let's' signifies a suggestion or proposal.
• The reporting verb 'said to' changes to 'proposed to' or 'suggested to'.
• The conjunction 'that' is used, followed by the subject pronoun 'they'/'we' and the modal auxiliary 'should' + base verb ('that they should go for a picnic').