"when" in relative clauses

"when" functioning as a relative pronoun in a relative clause can only take the subject of the sentence? like in this example Recently documented examples of neurogenesis, the production of new brain cells, include the brain growing in mice when placed in a stimulating environment or neuro...

my doubt : while i do understand that A is wrong for many other reason but plz confirm whether the initial comparison in A is oki : While it costs about the same to run nuclear plants as other types of power plants ELLIPSIS is the omission of words whose presence is understood. Here, it is not crys...