[单选题]
An electron is moving ab vutrj dzh(1d4+ b.5k(+ ityv( ensxe0out a single proton gcszq: f8 d5w;q7drjao6haae14x k :) in an orbit characterized by n = 4. How many of the electron's de Broglie wavelengths fit into the circumferd6w; q s zaa8co xdkq7a1g :)fh4e:5jrence of this orbit?