The first question should be D 1 cm, and the second question should be expressed as 1.3E9 people by scientific notation.

(e is the notation of computer science, and the handwriting of 1.3E9 is 1.3 * 10 9. )

Scientific notation, which represents a large number as a * 10 n, where the absolute value of a is greater than or equal to 1 and less than 10. N equals the number of integer digits minus one.

Of course, scientific counting can also represent smaller numbers. For example, 0. 1 can be expressed as 1 * 10- 1.