What can be the subject complement (主詞補語)?  

  a. Noun and Pronoun: 

     For example:   David Smith is our new teacher (noun).

                               S         Vi          SC 

                         Our new teacher is  David Smith  (pronoun).                                               

                                  S            Vi       SC

  b. Adjective,  Present Participle and Past Participle: 

     For example:    She looks great (adjective). 

                                  S      Vi     SC

                         She looks enjoying the music 

                              (present participle phrase).

                          S     Vi        SC

                         She looks beat (past participle phrase). 

                          S    Vi      SC 

  c. Infinitive or Gerund 

      (used as a noun or noun phrase):

    For example:   His job is to serve the guests  

                                      (infinitive phrase).

                                  S      Vi       SC

                             His job is cleaning the dishes  

                                            (gerund phrase). 

                                   S     Vi        SC

 d. Noun Clause:  

    For example: 

     The reason for his delay was  that he had a flat tire this morning  

                                                          (noun clause). 

                   S                   Vi              SC