[单选题]
An electron is moving about a single proton in ohiw wryd 6h;t8 6*ti3an orbit charactogzd)c -pvw,1 m0rw b tf18un8erized by n = 4. How many of the electron's de Broglie wavelengths fit into the circumference of this n c)p8v m0, 1o1d-8zrwufgbw torbit?
