Fact 1: Aruler is used for measuring the length of an object.

Fact 2: With another ruler, measure the length of the shadow.

Given the two facts above, answer the question "How can you measure a shadow?" with the following options: 
- size
 - observe it
 - Light
 - simple
 - a ruler
 - mirrors
 - Winter
 - an image


 

     a ruler    