Explanation:

• - Option 1: By descent - Indian citizenship can be acquired by descent if either of the parents is an Indian citizen at the time of the child's birth.
• - Option 2: By Naturalisation - Citizenship can be granted through a legal process called naturalisation to a foreigner who has resided in India for a certain period and meets other criteria.
• - Option 3: By registration - Indian citizenship can be obtained by registration, subject to certain conditions, for individuals of Indian origin or people married to Indian citizens, among others.
• - Option 4: By Birth - Indian citizenship can be acquired by birth, if born in India under certain specified conditions.
• Correct Answer: Option 4: All of the above