Which of the following statements is CORRECT?

a$.$ Operating cash flow $($OCF$)$ is defined as follows:

OCF$=$EBIT$(1-T)-$ Depreciation and Amortization.

Free cash flow $($FCF$)$ is defined as follows:

$FCF=$EBIT$(1-T)$

$+$ Depreciation and Amortization

$-$ Capital expenditures required $to$ sustain operations

$-$ Required changes $in$ net operating working capital.

c$.$ Free cash flow $($FCF$)$ is defined as follows:

$FCF=$EBIT$(1-T)+$ Depreciation and Amortization $+$ Capital expenditures.

d$.$ Operating cash flow is the same as free cash flow $($FCF$).$