Both examples have similar argument structures, except for one feature ... Only one of them in each structure needs the WH-operator as a host. The other cannot have one as a host. The situation is ...
An example of a lexical predicate modifier is an adverb: (5b) shows that (4) is an argument of SUDDENLY. (5b) may be represented in the following tree structure: An eventuality (Bach: 1981) contains ...