Walking to school is a moderate distance, measured in kilometres (km).<br><br>
&bull; 2 cm is too small (about the width of a finger).<br>
&bull; 2 m is too short (about the length of a bed).<br>
&bull; kg measures mass, not distance.<br>
&bull; 2 km is a typical walking distance to school.<br><br>
Final Answer: D: km