Question

select the best evidence to support the statement that it’s not always easy to tell when a flood will occur.
floods are one of the most common hazards in the united states. flood effects can be local, impacting a neighborhood or community, or very large, affecting entire river basins and multiple states.
however, all floods are not alike. some floods develop slowly, sometimes over a period of days. but flash floods can develop quickly, sometimes in just a few minutes and without any visible signs of rain. flash floods often have a dangerous wall of roaring water that carries rocks, mud, and other debris and can sweep away most things in its path.
from federal emergency management agency, “are you ready?: an in - depth guide to citizen preparedness.”

Explanation:

To support the statement that it's not always easy to tell when a flood will occur, we look for evidence about the unpredictability of flood timing. The text about flash floods says they "can develop quickly, sometimes in just a few minutes and without any visible signs of rain". This shows that some floods (flash floods) have sudden, unnoticeable onset, making it hard to tell when they'll occur. The first paragraph is about the commonality and scale of floods, not their timing predictability.

Answer:

But flash floods can develop quickly, sometimes in just a few minutes and without any visible signs of rain.