A biologist exposes mice to mutagenizing X rays to generate an array of different mutants. He hopes to generate a mutant form of acetylcholinesterase that will be functional at normal body temperature but inactive at a higher temperature. Which step below would work as an initial screening step in the biologist's quest to eventually identify a mutant of this type?

Look for mice with normal muscle contraction–relaxation activity at normal body temperature that develop continuous muscle contraction during an induced fever.

Look for mice that develop hyperactivity and rapid muscle movements as their body temperature changes from normal to the higher temperature of an induced fever.

Look for mice with a normal response to loud noise that become more easily startled by the same noise stimulus as their body temperature rises during an induced fever.

Look for mice with normal muscle contraction–relaxation activity at normal body temperature that develop an inability to contract muscles during an induced fever.