The correct answer is:
An understanding of the number and size of leftover planetesimals in the early solar system.
The giant-impact hypothesis proposes that the Moon was created out of what was left of a collision between Earth and an astronomical body the size of Mars, around 4.5 billion years ago, in the Hadean eon. The heavy bombardment was a period when leftover planetesimals hit planets during the solar system's first hundred million years.
Haymarket, Homestead, and Pullman were all violent labor strikes.
The Homestead Strike occurred in 1892 in Homestead PA and was a violent battle between laborers and hired Pinkertons after a lockout.
The Haymarket Affair occurred in Chicago in 1896 and involved a violent labor protest and a bombing.
The Pullman Strike occurred in 1894 and was a nationwide violent railroad strike.
Answer: An early 20th - century reform movement seeking to return control of the government to the people, restore economic opportunities, and correct injustices in American life.
Explanation: I hope this helps.