For each calculation choose the correct answer written in standard form.
a) (7 * 10%) * (3 x 10)
А
B
21 x 100 21 x 10
с
2.1 x 10"
D
2.1 x 10
b) (2 * 10%) = (4 * 10)
А
2* 10
B
5 x 10
C
0.5 x 10
D
2 x 10