If simple sugars such as ribose and glycolaldehyde ________ Earth from elsewhere and survived impact--a possibility astrophysicist Nicolle Zellner outlined in a 2020 study--the sugars could have reacted with other molecules that were already present on the planet to form the nucleotides that are the structural components of RNA and DNA.
Which choice completes the text so that it conforms to the conventions of Standard English?
