If a planet existed whose mass and radius both half those of the earth, the acceleration due to gravity at its surface would be

• A.  \[\text{19}.\text{6 m}/{{\text{s}}^{\text{2}}}\]       
• B.  \[\text{9}.\text{8 m}/{{\text{s}}^{\text{2}}}\]
• C.  \[\text{4}.\text{9 m}/{{\text{s}}^{\text{2}}}\]                  
• D.  \[\text{2}.\text{45 m}/{{\text{s}}^{\text{2}}}\]