In active voice, the subject performs an action.
In passive voice, the subject receives an action.
The given sentence is in the active voice, as 'Ann' (subject) performs the action (has invited) towards the object (some of Ann's friends').
When you convert it to passive voice, the object (some of Ann's friends) now becomes the subject, and vice versa.
Option B: In this sentence, the new subject 'Some of Ann's friends) receives the action 'have been invited' by the new object.
Also, the tense of the given sentence is present perfect tense: has + past participle (invited). (It states that an action began in the past and has completed in the immediate past.)
As the tense does not change, and 'have been invited' is also the present perfect tense (passive form), B is the correct option.
Option A: 'Were invited' is in the simple past, whereas the sentence is in present perfect.
Option C: 'Are invited' refers to the simple present tense, not the required present perfect.
Option D: 'Had been invited' refers to past perfect tense.
Hence A, C and D are incorrect.