Explanation:

The correct answer is option D, "Devout". Let's understand why.

Meaning of the word "pious":
The word "pious" is an adjective that describes a person who is deeply religious, devout, and devoted to their religious beliefs and practices. It is often used to describe individuals who are sincere, reverent, and committed in their religious or spiritual devotion.

Differences between the given options:
Let's analyze the other options to understand why they are not the correct answers:

- Pure: While the word "pure" can sometimes be associated with religious purity, it does not fully capture the essence of the word "pious". "Pious" goes beyond purity and implies a deep sense of religious devotion and faithfulness.

- Pretentious: The word "pretentious" means attempting to impress others by pretending to be more important, intelligent, or cultured than one actually is. This is not an appropriate synonym for "piety" or "piety".

- Clean: The word "clean" refers to something that is free from dirt, stains, or impurities. It has no direct relation to the religious or spiritual devotion implied by the word "pious".

Why "Devout" is the correct answer:
The word "devout" is an adjective that perfectly captures the meaning of "pious". It describes a person who is deeply religious, committed, and faithful in their religious beliefs and practices. A devout person is dedicated to their religion, observes its rituals and traditions, and seeks to live in accordance with its teachings. They are sincere in their faith and show reverence towards their religious beliefs.

Conclusion:
In conclusion, the word "piety" is best represented by the option D, "Devout". This word encompasses the deep religious devotion, sincerity, and faithfulness associated with being "pius".