The correct option is C kilometre
The distance between two countries like India and Germany is huge. So, very large magnitude values would be needed to express the distance between two countries in millimetres, centimetres or metres.
The ascending order of different units of measurement of length is shown below:
millimetre < centimetre < metre <kilometre
From the given options, kilometre is the largest unit of measurement and more suitable for measuring distances between two countries.