A cyclist rides $d$ km at an average speed of $u$ km/h, and then rides a further $d$ km at an average speed of $v$ km/h. Which expression gives the average speed, in km/h, for the whole ride?

• A$\dfrac{u+v}{2}$
• B$\dfrac{2uv}{u+v}$
• C$\dfrac{uv}{u+v}$
• D$\dfrac{u+v}{2uv}$

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