Fact 1: Dilation occurs when cell walls relax.

Fact 2: Conversely, a decrease in light intensity causes dilation of the pupils.

Given the two facts above, answer the question "What can cause cell walls to relax?" with the following options: 
- Decreased light intensity
 - Something coming from a gland
 - matter vibrating
 - Temperature changing
 - Water vapor cooling
 - the Earth being tilted
 - raising their temperature
 - heat produced


 

 Decreased light intensity        