To research the claim that green tea lowers ldl (so-called bad) cholesterol, you ask a random sample of individuals to divulge whether they are regular green tea users or not. you also obtain their ldl cholesterol levels. finally, you compare the ldl cholesterol levels of the green tea drinkers to those of the non-green tea drinkers. explain why this is an observational study. a. this is an observational study because there is no intent to manipulate the explanatory variable, ldl cholesterol levels. b. this is an observational study because the researcher is manipulating the explanatory variable, whether the individual is a green tea drinker or not. c. this is an observational study because the researcher is manipulating the explanatory variable, ldl cholesterol levels. d. this is an observational study because there is no intent to manipulate the explanatory variable, whether the individual is a green tea drinker or not.