In "the deadliest tsunami in history" the cause of the indian ocean tsunami was
1.a rupture
2.an unintended explosion in japan
3. a tornado off the coast of sumatra
4. mass animals migrations to the north
in "the deadliest tsunami in history" survivors of the tsunami recognized that a receding ocean
1. was a sign of danger
2. left pollution everywhere
3. left boats and fish stranded on shore
4. signals a coming earthquake

The cause of the Indian Ocean tsunami was 1. a rupture.

Survivors recognized that a receding ocean 3. left boats and fish stranded on shore.

Explanation:

According to "The Deadliest Tsunami in History", published in 2004 by the National Geographic, the cause of the tsunami that killed over 150,000 people was an earthquake. The movement of two tectonic plates caused a rupture, moving trillions of tons of rocks under the ocean. The result was a deadly tsunami.

Unfortunately, survivors later said they did see the ocean receding prior to the tsunami, but weren't aware of the danger:

"[...] they had never seen the sea withdraw such a distance, exposing seafloor never seen before, stranding fish and boats on the sand. Tragically the novelty of the sight apparently stoked the curiosity of the people who ran out onto the exposed seafloor. Tourists in Thailand were seen wandering around photographing the scene."

From the excerpt above, we can note that survivors did not see the receding ocean as a sign of danger.

just say it's your friend did it and you had no idea?

it is the background information on the characters and setting explained at the beginning of the story. the exposition will often have information about events that happened before the story began. the exposition is often the very first part of the plot.