Express the following with appropriate units and significant figures: (a) $1.0 \mathrm{~m}$ plus $9 \mathrm{~mm}$, (b) $1.0 \mathrm{~m}$ times $1 \mathrm{~mm}$, (c) $1.0 \mathrm{~m}$ minus $998 \mathrm{~mm}$, and (d) $1.0 \mathrm{~m}$ divided by $998 \mathrm{~mm}$.