When doing curls, john is careful to extend through the full range of motion and quickly lock his elbows to make sure that he does not drop the weight. this is an example of

a.
a good technique because he moves quickly
b.
a bad technique because he moves through the range of motion
c.
a good technique because he is paying attention to form
d.
a bad technique because he quickly locks a joint

The right option is; D.  a bad technique because he quickly locks a joint

This is an example of a bad technique because he quickly locks a joint.

Locking the joints during exercise involves fully extension of the elbow or knee until it cannot straighten again. Locking the joints is a bad technique as it put an extensive amount of stress on the joint and away from the muscles, which can result in joint and muscle problems or injury.  

the answer is d

hope this and you do good