Yahoo! and Hotmail held onto their lead in email market share for several years after Gmail$$s introduction. It took Google $8$ years to finally top these $2$ early leaders. Google$$s ability to succeed after being late to the search and mobile party is:

a$.$

because firms have created differences that can be easily matched by rivals.

b$.$

a result of superior technology alone.

c$.$

an illustration of the low barriers to entry in the tech industry.

d$.$

an example of having a young CEO.

e$.$

a story about the failure of incumbents to monitor their competitive landscape, recognize new rivals, and react to challenging offerings.