B. Net working capital is calculated as current assets minus current liabilities. At January 1, current assets were $16 million and current liabilities were $7 million, giving a working capital of $9 million. At June 30, current assets were $18 million and current liabilities were $8 million, giving a working capital of $10 million. Thus, during the period, working capital increased by $1 million.

C. Working capital is current assets minus current liabilities. Total assets minus total liabilities, which is stockholders' equity, stayed the same. But working capital did not stay the same.

D. This answer does not include inventory as a current asset in the working capital calculation. See the correct answer for a complete explanation.