Final answer:
Kai is the one who has perfect form for a modified push-up according to Coach Cardio's criteria, with her knees and toes on the floor, back and legs straight, hands under her shoulders, and elbows bent to 90 degrees.
Step-by-step explanation:
Coach Cardio asks his class to do 5 perfect modified push-ups. Assessing the description of Jason, Joey, Kai, and Katie's push-up forms, we can determine who has the perfect form. According to the provided details, a perfect modified push-up involves having the knees and toes on the floor, legs and back in a straight line, hands under the chest or shoulders, and elbows bent to 90 degrees.
Kai meets all the criteria for perfect form in a modified push-up because her toes and knees are on the floor, her legs and back are in a straight line, her hands are under her shoulders, and her elbows are bent to 90 degrees. Neither Jason, Joey, nor Katie meets all these criteria as Jason's legs are not in the modified position, Joey's elbows are bent too sharply at 45 degrees, and Katie's back is not in the correct position as her rear end is over the knees.