Fact 1: Loud noises can cause animals to startle.

Fact 2: And at 4,000 rpm, highway engine noise is still plenty loud.

Given the two facts above, answer the question "What can startle animals?" with the following options: 
- pigeons
 - Electrical
 - Frogs
 - nothing
 - sunset
 - Movement
 - engines
 - sunrise


 

       engines  