[单选题]
The temperature of an ideal lnk, s 3*xd*yygas ilx7lkoxsc3o3uj /j 82;y y7tyncreases from $2 \; ^{\circ}C$ to $4 \; ^{\circ}C$ while remaining at constant pressure. What happens to the volume of the gas?
A. It decreases slightly.
B. It decreases to one-half its original volume.
C. It increases slightly.
D. It increases to twice as much.