Choice "D" is correct. The current ratio is current assets divided by current liabilities. The sale of land would increase cash and therefore current assets without increasing current liabilities. This would increase the current ratio. Furthermore, the sale of land at a loss would decrease net profit.
Choice "c" is incorrect. The payment of a tax payment would not decrease net profit because the expense was accrued last year.
Choice "b" is incorrect. The use of cash to retire a long-term bond would reduce current assets without reducing current liabilities. This would reduce the current ratio.
Choice "a" is incorrect. As above, this would reduce cash without reducing current liabilities.