which of the following charges of an oil drop was not determined by millikan in his experiment? (charge of electron is -1.60 x 10^-19 C).
A. -7.2 x 10^-19 C
B. -3.2 x 10^-19 C
C. -4.8 x 10^-19 C
D. -9.6 x 10^-19 C