The by phrases of passives behave like complements and can undergo the same type of extraction, as in ((151)).
Tree structures for this type of sentence are very similar to those for the
wh-extraction of NP complements discussed in section 13.3 and have the
identical important features related to tree structure and trace and inversion
features. The tree in Figure 13.4 is an example of this
type of tree. Topicalization of NP objects of prepositions is handled the same
way as topicalization of complement NP's.