The correct grammatical words that fit into the given sentence is “are waiting” because “the nurses, except Henry are waiting (simple presentence) in the conference room”.
The nurses are subjects and “are waiting” is correct form of sentences grammatically. The other words do not fit into the above sentences because they may form wrong grammatical sentences to read.
Thus, the options (d), (b) and (a) are incorrect.
The correct grammatical words that fit into the given sentence is “are waiting” because “the nurses, except Henry are waiting (simple presentence) in the conference room”.
Therefore, the correct option is – c. are waiting.