Question

thought an exhibition would cost great britain too much money. to help the locals feel better about the expenses of the project, prince albert decided the fair would charge visitors an entrance fee. this would help pay for the cost of having such a big exhibition.
prince albert wanted to dazzle the public with the building where the exhibition would be held. so he made the unique choice of hiring a greenhouse maker to design a structure with glass walls and ceilings. it became known as the crystal palace. it was so massive that if you walked past all the displays, youd have walked eight
miles
years
steps

Explanation:

The text describes the massive size of the Crystal Palace exhibition space. "Miles" is the only unit that logically fits the context of walking past all displays in a huge structure, as "years" refers to time and "steps" is too small a unit for the scale described.

Answer:

miles