Answer:
d. The purpose of this research is to study how childhood experiences are related to risk of depression.
Explanation:
This answer satisfies the requirements of the question as it uses mild language that will not scare off respondents while also maintaining transparency and truthfulness. This can be seen in wordings such as;
a. Childhood experiences: Instead of explicitly using the term child-hood abuse which can scare off respondents, this phrase uses a milder form of the word that is also not dishonest in itself.
b. Risk of depression: Instead of using heavy terms such as "severe depression," or shady terms like "bad expreciences," the phrase, "risk of depression," helps the subjects to honestly identify what the question is about in a mild way.