Select the most appropriate option to fill in the blank.

He had hardly gone a few kilometres ______ his car broke down.

when

The correct option to fill in the blank is when.

The sentence is about the car breaking down after only a few kilometers. The word "when" is used to indicate a time when something happened.

The other options are incorrect.

• That is used to introduce a clause that provides additional information. In this sentence, the clause "that his car broke down" is not providing additional information, but is instead stating the main event of the sentence.
• Where is used to indicate a place. In this sentence, the place is not important, so the word "where" is not appropriate.
• Than is used to compare two things. In this sentence, the car is not being compared to anything, so the word "than" is not appropriate.