Question

complete
when it is cold, shivering causes
the muscles to □ and
produce □.
done ✓

Explanation:

In cold conditions, shivering is a physiological response. Muscles contract rapidly during shivering, and this process of muscle contraction (a form of movement) generates heat as a by - product to help maintain body temperature. So the first blank should be "contract" and the second blank should be "heat".

Answer:

First blank: contract; Second blank: heat