The best answer is **D. norm**.

**Explanation:**
The phrase "delaying parenthood is slowly becoming the _ in some communities" suggests that the practice of postponing having children is increasingly accepted or common in those communities. The word "norm" refers to a standard or typical pattern of behavior that is accepted within a particular group or society.

- **A. specialty** implies something unique or specialized, which doesn't fit the context of common practice.
- **B. confusion** suggests a lack of clarity or understanding, which is also irrelevant here.
- **C. festivity** indicates celebration or a joyous event, which does not apply to the serious topic of parenthood.

Thus, "norm" accurately reflects the idea that delaying parenthood is becoming a typical behavior in certain communities.