The correct answer is A. Sandy said that she had already written a letter to her family.
Sandy’s statement, “I have already written a letter to my family,” is in the past perfect tense. This tense is used to talk about an action that happened before another action in the past. In this case, Sandy is talking about an action (writing a letter to her family) that happened before another action (saying the statement).
The other options are incorrect because they do not use the past perfect tense. Option B, “Sandy said that she wrote a letter to her family,” is in the simple past tense. This tense is used to talk about an action that happened at a specific time in the past. Option C, “Sandy said that she was writing a letter her family,” is in the present progressive tense. This tense is used to talk about an action that is happening now or that is happening repeatedly. Option D, “Sandy said that she will write a letter to her family,” is in the future tense. This tense is used to talk about an action that will happen in the future.