need only types answer please

The following table shows the calculation of basic and diluted net income per share attributable to Gilead common stockholders (in millions except per share amounts):

The denominator for diluted earnings per share was increased by 13 million shares for the effect of options, while Gilead had more than 19 million options exercisable at 12/31/2016. What are factors that could explain the difference?

a. Some of the options are expected to forfeit

b. Some of the options are expected to expire

c. The denominator is increased by stock purchases under the treasury stock method

d. Some of the options are anti-dilutive and do not affect the denominator

e. All of the above

Year Ended December 31, 201620152014 Net income attributable to Gilead Shares used in per share calculation - basic 1,3391,4641,522 Effect of dilutive securities: Stock options and equivalents 13 23 33 Conversion spread related to the Convertible Notes 214 Warrants related to the Convertible Notes 4 20 62 Shares used in per share calculation - diluted \begin{tabular}{llllll} & 1,358 & & 1,521 & & 1,647 \\ \hline & & & & & \\ $ & 10.08 & $ & 12.37 & $ & 7.95 \end{tabular} Net income per share attributable to Gilead common stockholders - diluted $9.94$11.91$7.35