The following common$-$size income statement data and tax rates are available on a company.$$

Financial item

Current year $(\%)$

Revenues

$100$

Cost of goods sold

$37\mathrm{.}6$

Interest expense

$3\mathrm{.}0$

Research expenses

$4\mathrm{.}3$

Selling and general expenses

$31\mathrm{.}9$

Income tax rate

$20\%$

Prior year$$s profitability ratios

Gross profit margin

$61\mathrm{.}5\%$

Operating profit margin

$25\mathrm{.}8\%$

Net profit margin

$17\mathrm{.}8\%$

The profitability ratio that had the largest absolute increase in value in the current year is the:

a$.$

Operating profit margin

b$.$

Interest coverage ratio

c$.$

Net profit margin

d$.$

Gross profit margin

e$.$

Pretax profit margin