We traveled . . . . . . . . a boat to reach Sri Lanka.

Solution(By Examveda Team)

In this sentence, the appropriate preposition to use is "by".

The sentence "We traveled by a boat to reach Sri Lanka." indicates the means or mode of transportation used to travel from one place to another. The preposition "by" is commonly used to denote the mode of transportation or the method through which an action is carried out.

While prepositions like "about" and "for" may be suitable in different contexts, they do not convey the intended meaning of indicating the means of travel in this sentence.

Therefore, Option C: by is the correct preposition to complete the sentence appropriately.