The weightlifting program of Macheng Siyuan Experimental School is the traditional physical education class of the school. If it is for students to lift weights, here are some ideas about the competit

The weightlifting program of Macheng Siyuan Experimental School is the traditional physical education class of the school. If it is for students to lift weights, here are some ideas about the competition. A, students lift the barbell from the ground above their heads, students give the barbell an upward force, the barbell moves upward for a certain distance, and students do work on the barbell.

B, students lift the barbell over their heads for 3 seconds, students give the barbell an upward force, the barbell does not move upward, and students do no work on the barbell.

C. The barbell is at rest, and the gravity exerted by the barbell and the support of people for the barbell are a pair of balancing forces.

D. When the students are still on the platform, the gravity and supporting force received by the students are equal in magnitude and opposite in direction, acting on the same straight line and the same object, which is a pair of balancing forces. Does not conform to the meaning of the question.

So choose C.