A train runs x km at an average speed of \[{{k}_{1}}\]km/h and y km at an average speed of \[{{k}_{2}}\]km/h. The average speed of the train for the entire journey is:

• A. \[\frac{x+y}{{{k}_{^{1}}}+{{k}_{^{2}}}}km\text{/}h\]                                            
• B. \[\frac{{{k}_{^{1}}}{{k}_{^{2}}}(x+y)}{x{{k}_{2}}+y{{k}_{1}}}km\text{/}h\]
• C. \[\frac{x{{k}_{^{1}}}+y{{k}_{^{2}}}}{{{k}_{2}}+{{k}_{1}}}km\text{/}h\]                                                 
• D. \[\frac{xy({{k}_{1}}+{{k}_{^{2}}})}{x{{k}_{1}}+y{{k}_{2}}}km\text{/}h\]
• E. None of these