Since the sentence is missing I will tell you something helpful about academic style so you can find out yourself which sentence uses it and it is linear.
Academic style of writing has one central point, idea or theme and that is the most important thing of the academic text. It has an introduction, elaboration, and conclusion. In the introduction, we can find useful information about what is written about and in elaboration, we can see a description of the situation or something else. The conclusion is closing the text and central point.
It can be objective, formal, responsible, complex...
The answer is 'd' ,but the complete indirect object is 'her parents' not just 'parents' The indirect object always answers the question 'who'. Carol sent who? The answer is 'her parents' which is the indirect object.
