Rosa Watches Four Children Jumping

Rosa watches four children jumping. If they are all developing at the average rate, which child does Rosa identify as being three years old?

A) Wolfgang, who has both feet briefly off the ground when he steps off a step
B) Artie, who can execute a broad jump
C) Lucinda, who can jump over a 5-inch-tall block
D) Cydnee, who can jump forward on both feet 5 times in a row