A

Step 1: Bohr proposed that electrons move in specific orbits around the nucleus without radiating energy.
Step 2: According to the conservation of angular momentum, the angular momentum of an electron in these orbits is quantized.
Step 3: This means that the angular momentum can only take certain discrete values given by the formula: \( L = n \frac{h}{2\pi} \), where \( n \) is a positive integer and \( h \) is Planck's constant.
Step 4: This quantization leads to the idea of stable orbits and explains the discrete energy levels of electrons, which is a key aspect of Bohr's model.
Therefore, Bohr's use of conservation of angular momentum is fundamental to his explanation of atomic structure.