Read the passage.

excerpt from "marie curie and the discovery of radioactivity" by mara rockliff

the energy appeared to come from inside the metal itself, deep down at the level of its atoms. marie curie named this atomic energy radioactivity. a substance that emitted this energy was called radioactive.

her experiments yielded a second surprise. a sample of uranium-rich pitchblende turned out to be three or four times as radioactive as pure uranium. how could this be? marie had already tested every known element of pitchblende. none was radioactive. but something in that pitchblende, something besides the uranium, was sending out rays.

it could be inferred that the word emitted in the first paragraph means "released."

which context clue best confirm this meaning of the word emitted?

"turned out to be"

"three or four times as radioactive"

"deep down at the level of its atoms"

"sending out rays"