Data were collected on a random sample of 100 low birthweight, pre-term infants born in a large Boston (Massachusetts, US) teaching hospital. Infants in the sample had birthweights between 20 and 53 oz. One research question of interest was in regards to the association between head circumference at birth, and whether the mother suffered from toxemia (pregnancy induced hypertension) during the pregnancy. The following table shows the results of several linear regression models that estimate this association between head circumference (cm) and toxemia, both unadjusted, and adjusted for other characteristics of the infants, including birthweight (oz) and gestational age (weeks). (please note: only the slope estimates and standard errors for toxemia are shown for the models that also included other predictors) Regression Coefficient Standard Error of Model Predictors in Model (Slope) for Toxemia Regression Coefficient A Toxemia 0.82 0.62 B Toxemia, birthweight (oz) 0.76 0.37 C Toxemia, gestational age (wks) -1.41 0.41 D Toxemia, birthweight (oz) -0.52 0.37 gestational age (wks) `Toxemia is an indicator variable coded 1 if mother had toxemia, 0 if mother did not have toxemiaWhich of the following statements best describes the unadjusted mean difference (and 95% CI) in head circumference for infants whose mothers had toxemia versus infants whose mothers did not have toxemia? a. Infants born to mothers who had toxemia had average head circumference of 0.82 cm greater on average than infants born to mothers who did not have toxemia (95% CI -0.42 cm to 2.06 cm) b. Infants born to mothers who had toxemia had average head circumference of 0.82 cm smaller on average than infants born to mothers who did not have toxemia (95% CI -2.06 cm to 0.42) c. The estimated unadjusted mean difference in head circumference (and corresponding 95% confidence interval) cannot be estimated without the intercept from the simple linear regression model of head circumference regressed on toxemia. d. The mean difference in average head circumferences is statistically significant (a=0.05) as the 95% CI does not include 0