Review the passage:
Marcus has no consideration for the ecosystem rich with life in his backyard.
When he cuts the lawn, he slows for nothing. As
toads, lizards, and insects jump to the sanctuary of bushes to avoid the
deadly mower blades.
You chose the second part, When he cuts the lawn, he slows for nothing. This part has a main clause: the second he is the subject; slows is the verb. A fragment will not have a main clause.