Change into indirect speech: She said, "Let us go for a walk."
Correct: A
The verb 'let us' is used for suggestions. In indirect speech, it is commonly reported using 'suggested + verb-ing' or 'suggested that + subject + should + verb'. 'Suggested going for a walk' is the most concise and appropriate form. 'Suggested that we should go for a walk' is also acceptable, but 'suggested going for a walk' is the standard reporting form.