Which of the following expressions is written in scientific notation?

A. 73.4 X 10^5

B. 0.09 X 10^7

C. 80 X 10^3

D. 4.22 X 10^-5

Which of the following expressions is written in scientific notation?

A. 73.4 X 10^5

B. 0.09 X 10^7

C. 80 X 10^3

D. 4.22 X 10^-5