Read these passages from When Birds Get Flu and Cows Go Mad! by John DiConsiglio. "1918 The Superbug"

A deadly influenza bug—called the Spanish flu—kills 40 to 50 million people across the globe. More than 500,000 Americans die. The flu is spread by soldiers returning home from World War I.

"Spanish Flu Mystery May Be Solved!"

Atlanta—October 5, 2005

A team of scientists has solved an 87-year-old mystery. The cause of the 1918 Spanish flu, which killed 40 to 50 million people, has finally been identified.

What is the most likely reason the Spanish flu receives so much attention, both from the author of this article and from the scientists studying it?

because it killed so many people
because it relates to World War I
because it was spread by scientists
because it was the oldest unsolved case