Step 1: Understanding the sentence structure.
In the sentence "Bo doctorni thani thangkha", we are looking for a postposition. Postpositions are words that typically follow the noun or pronoun they relate to, instead of preceding it (like prepositions in English).
Step 2: Analyzing the options.
- (1) Bo: This is not a postposition; it’s the noun here.
- (2) Doctorni: This is a noun too, not a postposition.
- (3) Thani: This is also not a postposition, it functions as part of the sentence.
- (4) -ni: This is the correct postposition in the sentence, indicating a relational function.
Step 3: Conclusion.
The correct answer is -ni.