For each calculation choose the correct answer written in standard form.
a) (7 × 10⁵ ) × (3× 10²)
A 21 × 10¹⁰
B 21 ×10⁷
C 2.1 × 10¹¹
D 2.1 × 10⁸
b) ( 2 × 10⁵) ÷ ( 4 × 10² )
A 2 × 10 ³
B 5 × 10²
C 0.5 × 10³
D 2 × 10²
