What lesson can be learned from the example of Amazon winning competitive battles against weakened retailers and other companies such as Alphabet $($Google$)$ and Walmart?

a$.$ Ignoring competition will have no impact on a firm's performance.

b$.$ Firms should focus on forming strategic groups to increase competitiveness.

c$.$ Differentiating products is not important for maintaining a competitive advantage.

d$.$ Even highly successful firms must continuously analyze and understand their competitors to maintain market$-$leading positions.