Explanation

• The given sentence is in the present indefinite tense.
• The structure followed to change the voice of the present indefinite tense is 'object+ is/am/are+ V3+ by+ subject'.
• Therefore, the correct passive voice of the given sentence is 'An important announcement regarding the foreign policy is expected today.'
• Note: In the given sentence, subject is understood, hence, 'by+ subject (by us)' is not given in the passive voice.