The angular momentum of an electron in each of its orbits must be some multiple of:

wavelength

Planck's constant

velocity of light

circumference

The Bohr's proposal for the angular momentum of an electron in Bohr's model of the hydrogen atom is:

L = (n*h) / (2π), where n is the number of the energy level and h is the Planck's constant. This equation shows us the quantization of angular momentum of the electron. So the correct answer is the second one: Planck's constant.