**The Answer:**

The correct answer is option 'D' - Members of Parliament can express themselves in English, Hindi, or their mother tongue. This means that MPs have the freedom to use any of these languages to communicate their thoughts, opinions, and arguments in the Parliament.

**Explanation:**

1. **Parliamentary Language Debate in India:**
In India, the question of which language(s) should be used in the Parliament has been a matter of debate and discussion. The Constitution of India recognizes both English and Hindi as the official languages of the country. However, due to the linguistic diversity of India, many members of Parliament also prefer to use their mother tongue, which could be any of the numerous regional languages spoken across the country.

2. **Freedom of Expression:**
The freedom of expression is a fundamental right guaranteed by the Constitution of India. This includes the freedom to express oneself in a language of one's choice. Recognizing the importance of linguistic diversity and the need to accommodate the varied linguistic preferences of the MPs, the Parliament allows its members to express themselves in English, Hindi, or their mother tongue.

3. **Importance of English:**
English has been widely used as a language of communication in India since the colonial era. It continues to be an important language for official and legal purposes, as well as for communication among people from different linguistic backgrounds. Many MPs, especially those from non-Hindi speaking states, may prefer to use English to ensure that their message reaches a wider audience and is easily understood by all.

4. **Significance of Hindi:**
Hindi is the most widely spoken language in India and is the first language of a significant portion of the population. It is also one of the official languages recognized by the Constitution. Many MPs, particularly those from Hindi-speaking states, may choose to use Hindi to communicate their thoughts and ideas effectively to a larger section of the population.

5. **Mother Tongue Preference:**
India is known for its linguistic diversity, with hundreds of languages spoken across the country. MPs belonging to various linguistic communities may prefer to use their mother tongue to express themselves in the Parliament. This ensures that their message is accurately conveyed and resonates with their constituents who share the same language.

In conclusion, the members of Parliament in India have the option to express themselves in English, Hindi, or their mother tongue. This flexibility allows them to communicate effectively and ensures that the diverse linguistic preferences and needs of the MPs and their constituents are respected.