A

Test question analysis: Test participles to make attributive and fixed phrases. The fixed phrase forbidden sb to do sth prohibits someone from doing something. This sentence is in its passive voice. Those have a passive relationship with the verb invite, so the past participle phrase is used as an attributive modification of those. The meaning of the sentence: Except for the doctors and nurses invited by Dr. Hu, no one is allowed to enter the patient's room. Therefore A is correct.

Comments: The fixed phrase forbidden sb to do sth prohibits someone from doing something. When a noun and a verb form a passive relationship, the past participle is used as an attributive to modify the noun. When the two form an active relationship, the present participle is used as an attributive to modify the noun.