Use the Following Information for Questions

Use the following information for questions:
In a study of 900 European American children born in 1991 ("Maternal Employment and Child Cognitive Outcomes in the First Three Years of Life: The NICHD Study of Early Child Care," Brooks-Gunn, Han, and Waldfogel, Child Development 73[2002]: 1052-1072) , the authors wrote "children whose mothers worked at all by the ninth month of their life had lower [cognitive outcome] scores at 36 months than did children whose mothers did not work by that time." These results were statistically significant.
-Can a conclusion be made that mothers who worked during the first nine months after having a child caused the lower scores seen at 36 months?

A) A cause and effect relation might be concluded because of the large sample size and the long follow-up period (3 years) .
B) A cause and effect relation might be concluded because the results were statistically significant.
C) A cause and effect relation cannot be concluded because the study was an observational study.
D) A cause and effect relation cannot be concluded because the study was a case-control study.