Which of the statements about Google's strategy and competitive environment is true?

a$.$

Brin and Page founded Google in their $20$s$,$ following Yang and Filo of Yahoo $($also in their $20$s$),$ underscoring just how easy it is for newcomers to create new threats in today's search market.

b$.$

The scale of server farms capable of indexing today's Web represents a significant barrier to entry.

c$.$

Google has invested in proprietary components such as chips and hard drives, creating a difficult$-$to$-$copy barrier to entry to any firm seeking to enter its markets

d$.$

Bing has been gaining significant market share on Google due to Microsoft's successful leverage of existing products $($Xbox$,$ Windows Phone, Office, and the Windows operating system$)$ as a default distribution channel for its search.

e$.$

All of the above are true.