It _______it is parents responsibility to take good care of their children. A. commonly says that B.  commonly to be said that C. is commonly said that D. is commonly saying

Để hoàn thành câu hỏi trên, ta cần điền vào chỗ trống một cụm từ đúng trong các lựa chọn đã cho. Đúng cách là sử dụng cấu trúc bị động "It is commonly said that" để giới thiệu quan điểm chung.

Vậy câu trả lời cho câu hỏi trên là:
C. is commonly said that.

In passive voice constructions, the subject of the sentence receives the action, which makes 'is commonly said that' the most appropriate choice.

Option D is incorrect because 'is commonly saying' does not fit in the sentence.

Option B is incorrect because the phrase 'commonly to be said that' is not a grammatically correct structure.

Option A is incorrect because the subject 'it' is missing in the sentence.