A debt ratio of $0\mathrm{.}9$ means

the firm has $$0\mathrm{.}90$ of short$-$term debt per $$1\mathrm{.}00$ of long$-$term debt.

the firm has $$0\mathrm{.}90$ of short$-$term debt per $$1\mathrm{.}00$ of assets.

the firm has $$0\mathrm{.}90$ of total debt per $$1\mathrm{.}00$ of equity.

the firm has $$0\mathrm{.}90$ of total debt per $$1\mathrm{.}00$ of assets.