How are ac and dc generators different?
in dc generators, commutators produce direct current.
in ac generators, no commutators or slip rings are used.
in dc generators, slip rings produce direct current.
in ac generators, commutators produce alternating current.

b. latent learning (the word "latent" itself means something that exists but isn't obvious, only under certain conditions! )

there is no correct list among the choices you've provided.

the list might look something like this:

-- baby human

-- piccolo

-- flute

-- soprano singer

-- trumpet

-- tenor singer

-- trombone

-- baritone singer

-- baritone horn

-- bass singer

-- tuba

since i had to make up the list myself, i made it easy on myself, and i didn't try to shuffle the string instruments and woodwinds into it too.