In each of the following situations, is it more reasonable to simply explore the relationship between the two variables or to view one of the variables as an explanatory variable and the other as a response variable? In the latter case, which is the explanatory variable and which is the response variable? (a) The weight of a child and the age of the child from birth to 10 years. (b) High school English grades and high school math grades. (c) The rental price of apartments and the number of bedrooms in the apartment. (d) The amount of sugar added to a cup of coffee and how sweet the coffee tastes.