In the following passage, some words have been deleted. Read the passage carefully and select the most appropriate option to fill in each blank.
Astronomers have discovered 62 new moons orbiting the ringed planet Saturn. Though some of the moons had been (1)________ as early as 2019, it takes more than sighting an object close to a planet to (2) ________ it is a moon and not an asteroid making a brief close passage to that planet.
Performing a painstaking (3) ________ of matching objects detected on different nights over the course of 24 months, the team tracked 63 objects that they ended up confirming as moons. One of (4) ________ satellites was revealed back in 2021, with the remaining 62 moons gradually announced over the past few weeks.
Select the most appropriate option to fill in blank no. 2.