An analysis showed a sample to contain 0.00471 grams of lead. How many micrograms is this?
a. 0.471 µg
b. 4.71 × 10⁶ µg
c. 4.71 × 10³ µg
d. 4.71 × 10⁻⁶ µg
e. 4.71 × 10⁻² µg