If the Earth was formed billions of years ago, then why is this year still called as 2020?

The full name for our year is 2020 A.D., which stands for Anno Domini or "in the year of our Lord". This began at the birth of Christ. So, when we say we're in the year 2020, what we're really saying is that it's been 2020 years since the birth of Christ.

the correct answer is c.

for your question the answer would have to be france