Final answer:
The Lennon-McCartney song that reached No. 2 and is also the theme to a 1968 animated film is "Yellow Submarine".
Step-by-step explanation:
The Beatles had two Lennon-McCartney songs that reached No. 2 on the charts, and you're asking about the one that is also the theme to a 1968 animated film. The song in question is "Yellow Submarine", which is option a. Neither "Let It Be", "Yesterday", nor "Hey Jude" fit the description as they were not themes for that animated film. "Yellow Submarine" was indeed featured as the title for The Beatles' 1968 animated movie and is one of their most iconic songs.