Terrorist attacks on the United States is the answer.
On September 11, 2001 that was the day New York got attacked by terrorists. The Twin Towers were the ones that got affected, 2,996 people (maybe more) died during that attacked. The terrorists were one of the 2,996 people that died (19 of them died). more than 6,000 were injured that day.
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Subatomic particles
Explanation:
Grand unification theory or GUT is a model that tries to describe the universe.
Answer : The average speed of the sprinter is, 34.95 Km/hr
Solution :
Average velocity : It is defined as the distance traveled by the time taken.
Formula used for average velocity :

where,
= average velocity
d = distance traveled = 200 m
t = time taken = 20.6 s
Now put all the given values in the above formula, we get the average velocity of the sprinter.

conversion :
(1 Km = 1000m)
(1 hr = 3600 s)
Therefore, the average speed of the sprinter is, 34.95 Km/hr