Clenching the fingers to make a fist, then relaxing and straightening them is an example of followed by

Clenching the fingers to make a fist, then relaxing and straightening them is an example of :Flexion followed by extension
To put it simply, joint will become shorter during flexion and will become longer during extension. When he made a fist, he curled ul the joints in his hand, and when straightening the arm, he elongate the joint on his elbow

Ibelieve the answer is water and oil.