If You Compare All the Firstborns in Your Class to All

Multiple Choice

If you compare all the firstborns in your class to all the later-borns,what might influence the results,other than birth order?

A) Child-rearing practices have changed from those of long ago.
B) ​More females are firstborns and more males are later-borns.
C) ​Many firstborns come from one-child families.
D) ​The firstborns in your class are older than the later-borns.