In an experiment, it was found that the total charge on an oil drop was 5.93 x 10⁻¹⁸ C. How many negative charges does the drop contain?
a) 3.72 × 10⁶
b) 1.19 × 10⁶
c) 9.35 × 10¹⁷
d) 5.93 × 10⁻¹⁸