Final answer:
Angular momentum is crucial in affecting the shape of an accretion disc by causing material to orbit the central object, forming its flattened structure due to conservation of angular momentum as the nebula spins faster.
Step-by-step explanation:
The role that angular momentum plays in the shape of an accretion disc is significant. Angular momentum prevents the collapsing material from falling directly into the center by creating a force that causes the material to orbit the central object. Since the closer material to the center has less angular momentum, it falls in more directly; whereas, material at greater distances has higher angular momentum and therefore moves into an orbit, creating the flattened disc shape. As the nebula contracts, angular momentum conservation causes it to spin faster, much like a figure skater pulling in their arms. Over time, this effect causes the spinning nebula to flatten out into the shape of an accretion disc around the central object. Consequently, the correct answer to the question is (d) Angular momentum influences the disc's rotation and flattening.