A solid whose volume does not change with temperature floats in a liquid. For two different temperatures \[{{t}_{1}}\] and \[{{t}_{2}}\] of the liquid, fractions \[{{f}_{1}}\]and \[{{f}_{2}}\]of the volume of the solid remain submerged in the liquid. The coefficient of volume expansion of the liquid is equal to

• A. \[\frac{{{f}_{1}}-{{f}_{2}}}{{{f}_{2}}{{t}_{1}}-{{f}_{1}}{{t}_{2}}}\]         
• B. \[\frac{{{f}_{1}}-{{f}_{2}}}{{{f}_{1}}{{t}_{1}}-{{f}_{2}}{{t}_{2}}}\]
• C. \[\frac{{{f}_{1}}+{{f}_{2}}}{{{f}_{2}}{{t}_{1}}-{{f}_{1}}{{t}_{2}}}\]       
• D. \[\frac{{{f}_{1}}+{{f}_{2}}}{{{f}_{1}}{{t}_{1}}-{{f}_{1}}{{t}_{2}}}\]