In the "Johnny and Jimmy" Study by McGraw, Johnny (Who

In the "Johnny and Jimmy" study by McGraw, Johnny (who had learned skating earlier than Jimmy) had difficulties skating when he was 3 years of age. What did McGraw credit this finding to?

A) Boredom on Johnny's part
B) Attitudinal differences; Johnny had become reckless while Jimmy was cautious
C) Johnny's learning to ride the tricycle; the two tasks could not be maintained at the same time
D) Inhibition