The radii of two soap bubbles are r1 and r2. In isothermal conditions, two meet together in vaccum. Then the radius of the resultant bubble is given by [MP PMT 2001; RPET 1999; EAMCET 2003]

• A.             \[R=({{r}_{1}}+{{r}_{2}})/2\]
• B.                      \[R={{r}_{1}}({{r}_{1}}{{r}_{2}}+{{r}_{2}})\]
• C.             \[{{R}^{2}}=r_{1}^{2}+r_{2}^{2}\]
• D.                      \[R={{r}_{1}}+{{r}_{2}}\]