What Was the Result of Research Conducted by Whitehurst and Colleagues

What was the result of research conducted by Whitehurst and colleagues (1988) regarding training parents of 2- and 3-year-old children in a technique of interactive story reading?

A) After 1 month of such reading, children in the experimental group were 8.5 months more advanced on a measure of verbal expression than were children in the control group, despite the fact that the two groups were equal at the beginning of the study.
B) After 3 months of such reading, there was no differences noted between the experimental group and the control group.
C) After 1 month of reading, children in the control group were 8.5 months more advanced on a measure of verbal expression than were children in the experimental group.
D) After 3 months of such reading, children in both the control group and experimental group were similar on a measure of verbal expression.