The correct answer is D. norm.

Here's a breakdown of why:

• Norm: This means a standard or pattern of behavior that is typical or expected in a particular group or community. In the context of the sentence, it suggests that delaying parenthood is becoming the standard or expected behavior in certain communities.
• Specialty: This refers to a particular area of expertise or interest. It doesn't fit the context because it doesn't relate to the behavior of delaying parenthood.
• Confusion: This implies a state of being unclear or uncertain. It doesn't match the sentence's meaning, as delaying parenthood isn't typically associated with confusion.
• Festivity: This means a joyful celebration or merrymaking. It's completely unrelated to the topic of delaying parenthood.

D. norm

Giải thích: "Norm" có nghĩa là quy tắc hoặc tiêu chuẩn xã hội, trong khi các từ còn lại không phù hợp với ý nghĩa của câu. "Delaying parenthood" trở thành một thói quen phổ biến, nên "norm" là lựa chọn chính xác.