Answer:
the 2nd one
Explanation:
All other symbols are for Mathematics.
Observe to to gather facts, by paying close attention towards what you are working on.
meanwhile, reference is the act or process on reaching to your conclusion, based on facts you already know .
<span>
The conditions in tornado alley are more favorable. In the summer, the plains of middle US get increasingly hot which in turn, cause updrafts as well as thunderstorms. When hot air becomes unstable and rises it meets cooler air above the thunderclouds, which causes tornadoes.</span>
