Is not because… but because an idiom or can because be omitted?
ex:
Guitarist Jimi Hendrix and Robert Fripp shook left hands when they first met not because both were left handed but (Hendrix had his right arm) in a sling.
a) same
b) Hendrix’s right arm was
d)because Hendrix’s right arm was

thank you!

Yeah, you definitely want to follow “not because” with “but because.”